Glossary of geography terms
# Glossary of geography terms

This glossary of geography terms is a list of definitions of terms and concepts used in geography and related fields, including Earth science, oceanography, cartography, and human geography, as well as those describing spatial dimension, topographical features, natural resources, and the collection, analysis, and visualization of geographic data. Related terms may be found in glossary of geology, glossary of agriculture, glossary of environmental science, and glossary of astronomy.

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## A

### absolute location

    The particular location of a point on Earth's surface that can be expressed by a grid reference such as latitude and longitude.

### accessibility

    A locational characteristic that permits a place to be reached by the efforts of those at other places.

### accessibility resource

    A naturally emergent landscape form that eases communication between areas.

### acme

    See summit.

### active volcano

    A volcano that is currently erupting, or one that has erupted within the last 10,000 years (the Holocene) or during recorded history.

### adret

    The sunny, warm aspect of a hill or mountain, as opposed to the ubac or shady side.

### affluent

    See tributary.

### agricultural geography

    A sub-discipline of geography which studies the spatial relationships between humans and agriculture, as well as the cultural, political, and environmental processes that lead to parts of the Earth's surface being transformed into agricultural landscapes through primary sector activities.

### alluvial fan

    A distinctly triangular or fan-shaped deposit of sediment transported by water, often referred to as alluvium. Alluvial fans usually form at the base of mountains, where high-velocity rivers or streams meet a relatively flat area and lose the energy needed to carry large quantities of sediment, which ultimately spreads out in all available directions. They tend to be larger and more obvious in arid regions.

### alluvial plain

    A wide, flat, gently sloping plain created by the long-term deposition of alluvium from one or more rivers flowing from highland regions, and typically characterized by various fluvial landforms such as braided streams, terraces, and meanders. Alluvial plains encompass the larger area over which a river's floodplain has shifted through geological time.

### alluvial soils

    Soils deposited through the action of moving water. These soils lack horizons and are usually highly fertile.

### alluvium

    Clay, silt, gravel, or similar detrital material deposited by flowing water.

### alpine

    Characteristic of or resembling the European Alps, or any other high-elevation mountain range or mountainous environment (especially one deeply modified by glacial erosion so as to contain characteristic landforms such as cirques, horns, etc.), in topography, climate, or ecological communities.

### altitude

    The height of an object in the atmosphere above sea level. The term is sometimes used interchangeably with elevation.

### amphidromic point

    A geographical location where there is little or no tide, i.e. where the tidal amplitude is zero or nearly zero because the height of sea level does not differ significantly at high tide and low tide, and around which a tidal crest circulates once per tidal period (approximately every 12 hours). The tidal amplitude increases, though not uniformly, with distance from these points. Amphidromic points are the consequence of resonance phenomena which occur when obstructing landmasses reflect tidal bulges back and forth across oceanic basins; their precise locations, usually in the open ocean near the center of the basin, depend largely on the surrounding topography and bathymetry, and also vary slightly with winds, currents, and the positions of the Sun and the Moon. There are at least a dozen well-defined amphidromic points across the Earth's oceans.

### anastomosing stream

    A stream or river composed of multiple, branching, interconnected, coexisting channels that enclose floodbasins on alluvial plains, usually formed when a slow-moving river encounters avulsions that divert its flow, creating new channels on the floodplain.

### anecumene

    The part of the Earth's surface which is uninhabited and/or uninhabitable by human beings. Contrast ecumene.

### angle of repose

    The steepest angle of descent or dip, relative to the horizontal plane, at which a mass of loose, freely movable material such as sand or unconsolidated rock debris can remain stationary, i.e. without sliding downward, despite the pull of gravity.

### Antarctic

    The region of the Earth that is south of the Antarctic Circle.

### Antarctic Circle

    The southernmost of the Earth's two polar circles of latitude, south of which the sun appears above the horizon for 24 continuous hours at least once per year (and is therefore visible at midnight) and also appears at least partially below the horizon for 24 continuous hours at least once per year (and is therefore not visible at noon). Its latitude is approximately 66°33′47.1″ south of the Equator. Contrast Arctic Circle.

### antecedent stream

    A stream or other watercourse that existed before the present form of the surrounding land surface was established and which maintains its original course and pattern despite changes in the local geology or topography. For example, a landscape featuring a river with a dendritic drainage pattern may be altered by gradual, localized tectonic uplift, but the river may be sufficiently powerful to erode through the new obstructions as rapidly as they are formed, carving a gorge rather than being redirected, and thereby preserving its dendritic pattern even though it now flows over a landscape that typically produces very different drainage patterns. Compare insequent stream.

### anthropization

    The conversion of open spaces, landscapes, and natural environments by human action.

### anthropogenic

    1. Of or relating to anthropogeny, the scientific study of the origins of human beings.
    2. Having an origin in human activity; caused by or attributable to humans.

### anti-dip stream

    A stream flowing in a direction approximately opposite to that of the dip of the underlying surface rocks. It is frequently, though not necessarily, an obsequent stream.

### anticline

    A geological upfold that has an arch-like convex shape and its oldest beds near its center, often visible at the Earth's surface in exposed rock strata. Contrast syncline.

### antimeridian

    1. The meridian of longitude that is directly opposite or antipodal to a given meridian, i.e. the imaginary line that is exactly 180 degrees of longitude distant from the given meridian. Together, a meridian and its antimeridian form a great circle that passes through the geographic poles.
    2. The 180th meridian in particular, i.e. the meridian of longitude that is exactly 180 degrees both east and west of the Prime Meridian, with which it forms a great circle dividing the Earth into the Eastern and Western Hemispheres. The 180th meridian is used as the approximate basis for the International Date Line because it mostly passes through the open waters of the Pacific Ocean.

### antipodes

    Any pair of points on the Earth's surface that are diametrically opposite to each other, such that a straight line connecting them would pass through the Earth's center. Such points are as far away from each other as possible, with the great-circle distance between them being approximately 20,000 kilometres (12,000 mi).

### anywhere fix

    A geographic position which a GPS receiver is able to calculate without requiring information about its own location or the local time.

### apogean tide

    The tide when the Moon is at its furthest distance from Earth in its orbit (its apogee), during which its gravitational pull is reduced, resulting in a smaller tidal range than is usual, i.e. lower high tides and higher low tides. Contrast perigean tide.

### apparent place

    The apparent position of an object in space as seen by an observer, which, because of physical and geometric effects, may differ from the object's true position.

### applied geography

    The application of geographical knowledge and techniques to the solution of economic and social problems on any scale, ranging from local to global, in disciplines such as civic planning, land use and management, location policy, and population studies, among many others.

### apposed glacier

    A glacier resulting from the merging of two separate glaciers.

### apron

    A spread of alluvium deposited by streams, especially those originating from a melting glacier. See also alluvial fan and outwash plain.

### aquiclude

    A normally permeable rock, underlying or overlying an aquifer, which becomes impermeable because of the saturation of its pores by water, potentially creating a confined aquifer.

### aquifer

    An underground layer of water-bearing permeable rock, rock fractures, or unconsolidated materials such as gravel, sand, or silt, which is sufficiently porous to carry or conduct water yet also sufficiently coarse or non-absorptive to release the water and thereby permit its exposure to or access from the ground surface. Groundwater from aquifers may naturally emerge at the surface, e.g. at a spring, or may be extracted using man-made wells. There are many different types of aquifer with various levels of hydraulic conductivity.

### aquifuge

    An impermeable rock stratum which not only obstructs the passage of water but cannot absorb it, e.g. granite.

### aquitard

    A bed or layer of rock that slows the conveyance of water from an aquifer due to its low permeability or low hydraulic conductivity.

### archipelago

    A collection of islands in a sea.

### arête

    A sharp, narrow mountain ridge, often resulting from the erosive activity of alpine glaciers flowing in adjacent valleys.

### arroyo

    A deep gully cut by a stream that flows only part of the year; a dry gulch. The term is used primarily in desert areas in North America and South America.

### Arctic

    The region of the Earth that is north of the Arctic Circle.

### Arctic Circle

    The northernmost of the Earth's two polar circles of latitude, north of which the sun appears above the horizon for 24 continuous hours at least once per year (and is therefore visible at midnight) and also appears at least partially below the horizon for 24 continuous hours at least once per year (and is therefore not fully visible at noon). Its latitude is approximately 66°33′47.1″ north of the Equator. Contrast Antarctic Circle.

### ash

    Fragments of lava or rock less than 1⁄3 centimetre (0.13 in) in diameter that have been ejected into the atmosphere by a volcanic explosion.

### aspect

    The direction toward which a slope faces with respect to a compass or to the Sun's position in the sky, or the direction which a segment of coastline faces as it meets the sea.

### Atlantic Seaboard fall line

    The physiographic border between the Piedmont and Atlantic coastal plain regions of eastern North America. The name derives from the river rapids and waterfalls that occur as the water flows from the hard rocks of the higher piedmont onto the softer rocks of the coastal plain.

### Atlantic-type coastline

    See discordant coastline.

### atlas

    A bound collection of maps.

### atmosphere

    The mixture of gases, aerosols, solid particles, and water vapor that envelops the Earth.

### atoll

    A ring-shaped coral reef that partially or completely encircles a lagoon.

### autonomous height

    See topographic prominence.

### aven

    A vertical or inclined shaft connecting a cave passage to the surface.

### avulsion

    1. The sudden loss of land by the action of water.
    2. The rapid abandonment by a river or stream of an existing channel in favor of the formation of a new channel, typically because the new channel follows a steeper or less obstructed course.

### awareness space

    All of the locations of which an individual is "aware", i.e. about which they have knowledge above some minimum level, even those they may not have actually visited. Awareness space includes activity space, and it enlarges as new locations are discovered and new information is gathered. See also search space and mental map.

### axis

    1. (coordinate system) Any of the reference lines of a Cartesian coordinate system, from which the signed distances to each coordinate are measured, e.g. the x-axis or the y-axis.
    2. (of a fold) The imaginary central line or plane dividing the limbs of the fold as symmetrically as possible; the crest from which strata dip downward and away in an anticline, or the lowest depth of the trough from which strata rise in opposite directions in a syncline.
    3. (of the Earth) The rotational axis of the Earth: the diameter between the North Geographic Pole and the South Geographic Pole, passing through the planet's geometric center, around which the Earth rotates anti-clockwise (i.e. to the east) once every 23 hours and 56 minutes. This axis is constantly tilted at an angle of about 66°30' with respect to the plane of the Earth's orbit around the Sun, which is the primary cause of the seasonal weather cycles experienced at temperate and polar latitudes.

### ayre

    Another name for a shingle beach or other gravel-covered spit, bar, or tombolo, used primarily in the archipelagos of northern Scotland.

### azimuth

    The angle formed between a reference vector (often magnetic north) and a line from the observer to a point of interest projected perpendicularly to the zenith on the same plane as the reference vector. Azimuth is usually measured in degrees and can be determined with a compass.

### azimuthal projection

    A map projection in which all bearings are laid off correctly from the centerpoint of the map, so that all points on the map are true in distance and direction from the center.
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## B

### backcountry

    Any geographical area that is remote, isolated, undeveloped, or difficult to access, as contrasted with frontcountry; sparsely populated or uninhabited wilderness. See also bush.

### backshore

    The part of a seashore lying inland from the mean high water line, landwards of the foreshore, from which it is often delineated by the presence of a strandline. This part of the beach is only affected by waves during exceptional high tides or severe storms.

### backslope

    The part of the profile of a hillslope that forms the steepest, typically linear portion of the slope, generally located in the middle and bounded by a convex shoulder above and a concave footslope below. The backslope may or may not include vertical or near-vertical cliffs.

### backwash

    The seaward return flow of a receding wave after it has broken on a beach or other surface. Contrast swash.

### backwater

    1. A part of a river in which there is little or no current, especially a side channel, a sluggish meander, or a slowing and widening of the main stem created by an obstruction to flow.
    2. A place regarded as remote, underdeveloped, or culturally backward relative to other places; a place or state of stagnation, in which little or no economic, social, or intellectual progress occurs.
    3. A secluded, peaceful place.

### badia

    In the Middle East, an arid area characterized by low or irregular precipitation and little or no vegetation.

### badlands

    An area of rugged or irregular topography resulting from extensive wind and water erosion of unconsolidated sedimentary rock.

### bajada

    A series of adjacent alluvial fans coalescing in a basin at the foot of a mountain range.

### Balkanization

    The political fragmentation of a larger region or state into multiple smaller regions or states, often implying mutual hostility or lack of cooperation between such units, as has occurred frequently in the Balkan Peninsula of southeastern Europe.

### bank

    1. The land alongside a body of water, particularly the sloping ground bordering and defining the channel of a flowing watercourse such as a river or stream.
    2. An elevation in the bed of a river, stream, or shallow sea, either fully or partially submerged, mid-channel or connected to the shore, and usually made of sand, mud, gravel, or other loose sediment. See also bar and shoal.
    3. Another name for a hill or hillside.

### bankfull stage

    The stage during which the channel of a river or stream is completely filled with water from bank to bank, immediately preceding the overbank stage, when the river overflows its banks and inundates the surrounding floodplain.

### bar

    An elevated area of unconsolidated sediment such as sand or gravel which has been deposited by the flow of a river or other moving body of water. See also shoal.

### barrage

    An impoundment built for seasonal floodwater storage and/or to create a reservoir for irrigation, as opposed to a dam, which instead serves the purpose of hydroelectric power generation, though at the broadest level the terms may be used more or less interchangeably.

### barrier island

    A long, narrow ridge or shoal lying above the highest high tide level (thereby creating an island) and parallel to the mainland coast, from which it is separated by a lagoon. Barrier islands are analogous to very large sandbars deposited naturally by wave and tidal action, often in extensive chains along the coastline, but may also be created artificially by dredging. Though their size and shape change frequently, particularly during storms, they are important natural breakwaters which shelter areas of relatively calm waters where wetlands and marine life flourish. See also spit and tied island.

### barrier reef

    A coral reef lying parallel to a shore and some distance from it, creating a sheltered lagoon which the reef protects from the open ocean.

### barrier ridge

    Any steep, unnavigable ridge or escarpment isolating one terrain from another.

### barrio

    In the Spanish-speaking world, a neighborhood or community within a larger urban area, generally with informal boundaries, though in some places the term may refer to a formal subdivision of a municipality.

### barrow

    See tumulus.

### barysphere

    The Earth's core and mantle considered together, i.e. all of the Earth's interior beneath the lithosphere.

### base level

    The lowest level to which a stream can erode its bed. The ultimate base level of all streams is the sea.

### baseline

    An accurately measured line of known length on the Earth's surface, used as a base or reference line in triangulation and other surveying operations.

### basin

    Another name for a depression, particularly one that is approximately circular, level or nearly level at the bottom, and/or surrounded on all sides by land of uniform elevation.

### batholith

    A very large body of igneous rock, usually granite, which has been exposed by erosion of the overlying rock.

### bathymetry

    1. The measurement of water depth, mainly of seas and oceans but sometimes of deep lakes.
    2. The study and depiction of the physical features or relief of the floor of a lake or ocean. In this sense bathymetry is considered the underwater equivalent of hypsometry or topography.

### bay

    A coastal body of water that is directly connected to but recessed from a larger body of water, such as an ocean, sea, lake, or another bay. The land surrounding a bay usually shelters it from strong winds and waves, making bays ideal places for ports and harbors.

### bayou

    In the southern United States, a sluggish or stagnant slough or backwater, or a marshy outlet of a lake or river.

### beach

    A landform along the shoreline of an ocean, sea, lake, or river with a loose surface of sand, gravel, shingle, pebbles, shells, stones, or coral.

### bearing

    The direction or position of an object, or the direction of an object's movement, relative to a fixed point. It is typically measured in degrees and can be determined with a compass. By convention, magnetic north is defined as having a bearing of zero degrees.

### bedrock

    The solid rock in the Earth's crust that underlies all soil and other loose material; the rock material that breaks down eventually to form soil.

### belt

    A large region or district (often but not necessarily a broad, elongated area of vague or indeterminate boundaries) identified or associated with one or more particular, distinctive characteristics, e.g. of climate (banana belt), vegetation (Pine Belt), topography (Alpide belt), geology or mineral resources (Lead Belt), agriculture (Corn Belt), land use (green belt), language or ethnicity (Hindi Belt), or social/cultural demographics (Bible Belt). See also regionalism.

### bench

    A narrow step, shelf, ledge, or terrace, typically backed by a steep slope, produced either naturally (e.g. by erosion, as with a wave-cut bench) or artificially (e.g. by mining).

### benchmark

    A surveying mark cut or embedded into a durable, fixed material, such as a rock or the wall of a building, for which the height above some designated datum level has been accurately measured.

### berg

    1. A mountain or hill; a cliff face or precipice.
    2. Another name for a bergschrund, iceberg, or inselberg.

### bergschrund

    A crevasse or series of parallel crevasses that opens in a glacier when a mass of moving ice detaches and pulls away from stagnant ice or firn. Bergschrunds are common in mountainous areas, often forming seasonally near the back of a cirque where the ice meets a steep or rocky headwall. When the rift forms directly between ice and rock, the gap is called a randkluft.

### berm

    1. A level space, shelf, or raised barrier separating two areas, often man-made and built of compacted earth. Berms often function as impoundments, fortification lines, or border walls and other lines of demarcation.
    2. A low, impermanent, nearly horizontal or landward-sloping shelf, bench, or narrow terrace on the backshore of a beach and parallel to the shoreline, formed by waves which deposit material beyond the average high water mark, e.g. during storms. Some beaches have no berms; others may have one or more.

### bight

    A bend or curve in a coastline, river, or other geographical feature typically indicating an especially large, open bay that is shallower than a sound.

### billabong

    In Australia, a branch of a river that is cut off when the main stem changes course, leaving an elongated and often ephemeral waterhole or oxbow lake.

### biological diversity

    A concept recognizing the variety of life forms in an area of the Earth and the ecological interdependence of these life forms.

### biogeography

    The study of the distribution of biological species and ecosystems in geographic space and through geological time.

### biogeosphere

    The outer part of the lithosphere, from the surface of the Earth to the greatest depth at which organic life can exist.

### biosphere

    The entirety of all biological systems on Earth, integrating all living beings and ecosystems; the realm in which biological organisms live.

### biota

    The animal and plant life of a region considered as a total ecological entity.

### blackwater

    The water of a slow-moving river channel flowing through a forested swamp or wetland, characterized by high concentrations of tannins leached from decaying vegetation, which results in a darkly stained color and high acidity.

### blowhole

    A hole or fissure, especially a nearly vertical one, that is the landward opening of a sea cave, frequently spouting or spraying air and seawater as waves crash against the cave's other opening.

### blowout

    A sandy depression formed when wind erodes into patches of bare sand on otherwise vegetation-stabilized sand dunes at the margins of coastal and arid ecosystems.

### bluff

    A steep slope or cliff marking the outer margin of a floodplain, especially one formed as the river erodes the concave bend of a meander. See also cut bank.

### bocage

    A landscape of mixed woodland and pasture, with fields and winding country lanes sunken between low, narrow ridges and banks surmounted by tall, thick hedgerows, especially as found in rural parts of western Europe.

### body of water

    Any significant accumulation of water, either natural or artificial, on the surface of the Earth. Bodies of water may hold or contain water, as with lakes and oceans, or they may collect and move water from one place to another, as with rivers, streams, and other watercourses.

### bog

    A type of wetland which accumulates deposits of dead plant material, especially mosses, known as peat. Bogs occur where the water at the ground surface is acidic and low in dissolved nutrients. They are one of four main types of wetland.

### bootheel

    See salient.

### border

    The geographical boundary of a political entity or legal jurisdiction, such as a country, state, or other subnational entity.

### bore

    1. (tidal) A steep-fronted wave formed by the convergence of two tidal bulges or by the constriction of an incoming tide as it travels up a river, firth, or narrow bay, temporarily reversing the direction of the current.
    2. (hole) A deep, man-made hole or shaft drilled into the ground, e.g. in mining, or for digging a well or tunnel.

### bornhardt

    A bald, steep-sided, dome-shaped hill, mountain, or rock outcropping at least 30 metres (98 ft) in height and several hundred meters in width. Compare inselberg, tor, and nubbin.

### borough

    A type of administrative subdivision in certain English-speaking parts of the world. Though traditionally used to refer to a fortress or a walled town, modern usage of the term can variably refer to any town with its own local self-government, a formal or informal subdivision of a large metropolis (as in New York City and London), or an entire administrative region (as in the U.S. state of Alaska).

### bottomland

    See floodplain.

### boulevardization

    The replacement of the narrow, congested, winding streets of an older town or neighborhood with wider, more modern streets or boulevards, often according to a carefully plotted grid layout.

### boundary

    Any line of demarcation, real or imaginary, visible or invisible, natural or artificial, with or without legal significance, which may be perceived from either or both sides of the line, indicating the place at which two or more geographical areas of distinct ownership, administration, legal jurisdiction, or any other quality meet; e.g. a border separating political or administrative divisions, zones of occupation, natural areas, or private and public property. See also frontier.

### bourne

    1. A seasonal or intermittent stream flowing from a spring in an otherwise dry valley, and whose flow depends on the level of the water table. The term is used primarily in the chalklands of southern England. See also winterbourne.
    2. The spring or fount itself.

### box canyon

    A short, narrow canyon with steep walls on three sides, allowing entry and exit only through the mouth of the canyon.

### brake

    See canebrake.

### brash ice

    See drift ice.

### breadbasket

    A region of a country or other polity which supports a large proportion of the country's domestic food production (especially of wheat and other grains) due to its fertile soils, favorable climate, and/or relative accessibility to agricultural interests.

### break

    1. Any more or less abrupt change in the profile of a slope, e.g. of a hillside.
    2. A heavily eroded area along a river featuring steep banks, bluffs, ravines, or gorges. The term is used chiefly in the plural (i.e. breaks) and primarily in the United States and Canada.

### break-in-bulk point

    A transfer point on a transport route where the mode of transport or type of carrier changes and where large-volume shipments are reduced in size. For example, goods may be unloaded from a ship and transferred to trucks at an ocean port.

### breakwater

    Any man-made structure built on the coast of a body of water, typically the sea, in order to reduce the intensity of wave action in an area adjacent to the shore, thereby providing safe harbourage for human activities in the inshore waters. Breakwaters may also be designed to protect the coastline from coastal erosion and longshore drift.

### brownfield land

    Any previously developed area of land that is no longer in use, often with derelict buildings and infrastructure, in some contexts implying land that has been abandoned because of pollution or contamination.

### brush

    Low-lying, woody, often dense vegetation or plant debris, e.g. scrub; a thicket of small trees and shrubs, or the plant community characterized by vegetation dominated by shrubs.

### built environment

    The human-made spaces that provide the setting for human activity, in which people live, work, and recreate on a day-to-day basis.

### burgh

    A type of administrative subdivision in Scotland and northern England, equivalent to a borough.

### burn

    In parts of the United Kingdom, Australia, and New Zealand, a large stream or a small river. See also bourne.

### bush

    Wild, undeveloped, or uncultivated land, especially when covered by thick shrubs and vegetation; sparsely populated or uninhabited wilderness. See also backcountry, hinterland, outback, and bushveld.

### bushveld

    In southern Africa, a tropical or subtropical woodland ecoregion consisting largely of open savanna with scattered trees; wild countryside as opposed to cultivated land.

### butte

    An isolated hill or mountain with steep or precipitous sides, usually having a smaller summit area than a mesa.

### bypass

    1. A route which diverges around a place rather than traveling through it, especially a road or footpath built specifically for the purpose of diverting automobile or pedestrian traffic away from areas that are congested, blocked, under construction, or unsafe.
    2. See flood bypass.
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## C

### cadastre

    A type of parcel-based land recording system containing a comprehensive record of interests in individual units of land within a country or other polity, usually including a geometric description of each parcel's physical location, dimensions, and boundaries that is linked to legal information detailing the nature of the interests (e.g. rights, restrictions, and responsibilities), the ownership or control of those interests, and the economic value of the land and its improvements. The cadastre is a fundamental source of data used in resolving disputes between landowners.

### cairn

    A man-made stack or mound of rocks, stones, or masonry, usually roughly conical or pyramidal in shape, constructed as a burial mound, to mark a surveyed point, or as a landmark or waypoint to aid routefinding on a route that is otherwise unmarked and difficult to distinguish from the surrounding environment.

### calanque

    A narrow, steep-sided valley surrounding an inlet formed in karstic regions along the Mediterranean coast, either by fluvial erosion or the collapse of the roof of a cave that has been subsequently partially submerged by a rise in sea level.

### caldera

    A large, cauldron-shaped depression that forms through the subsidence and collapse of a ground surface following the evacuation of an underlying magma chamber.

### campo

    1. In the Spanish-speaking world, the rural countryside or the bush.
    2. In Brazil, an area of level, open grassland with scattered trees, comparable to a savanna.

### canal

    A navigable artificial water channel, usually built as a conduit for human activity.

### canebrake

    A dense thicket of giant cane grasses, often lining a riverbank or other body of water. The term is used primarily in the southeastern United States.

### canyon

    A deep cleft between cliffs or escarpments, or a rift between two mountain peaks, resulting from weathering and the erosive activity of a river over long periods of geologic time.

### cape

    A large headland or promontory extending into a body of water, usually a sea or ocean.

### capillary fringe

    The soil layer lying immediately above the water table, in which water is drawn up and held within pore spaces by capillarity.

### capital

    1. A primary city or town of a country, state, province, or other subnational polity, especially one that is a seat of government for the entire polity, either by law or by virtue of being the physical location of the government's offices and meeting places, or both. A capital is often but not always the largest or most economically or historically important city of its constituent. A polity may have one or more capitals, or none.
    2. Any place considered to have informal primacy or importance with respect to some characteristic or association, e.g. Milan, Italy is sometimes unofficially called the "Fashion Capital of the World".

### caprock

    A stratum of erosion-resistant sedimentary rock (usually limestone) found in arid areas. Caprock forms the top layer of most mesas and buttes.

### cardinal directions

    The set of four primary directions used in cartography and navigation: north (N), south (S), east (E), and west (W). Together they form the primary divisions of the compass rose. They can be further subdivided into the intercardinal directions and secondary-intercardinal directions.

### carrying capacity

    The total number of human beings that an area can support given the quality of the natural environment and the level of technology of the population.

### cartography

    The study and practice of making maps and charts. A person who draws or makes maps or charts is called a cartographer.

### cartogram

    A map in which some thematic mapping variable, such as travel time, population, or gross national product, is substituted for traditional measures of land area or distance such that the geometry or space of the map is distorted in order to convey and emphasize the information of the alternate variable.

### cartouche

    A decorative panel or emblem on a map or a globe, enclosing the title, legend, scale, or any other information.

### castle koppie

    See tor.

### cataract

    A large waterfall, or a long series of rapids in a river, of the type occurring in the river Nile.

### catchment

    See drainage basin.

### causeway

    A track, road, or railway raised above a body of water or a low-lying place by virtue of being built upon a man-made embankment, typically constructed of earth, masonry, wood, or concrete. Compare bridge.

### cave

    Any naturally hollow underground space large enough for a person to enter.

### cavern

    A type of solutional cave that is formed in soluble rock with the ability to grow speleothems.

### cay

    A small, sandy, low-elevation island on the surface of an otherwise submerged coral reef; a type of coral island. Compare atoll.

### celestial pole

    Either of the two imaginary points in the sky at which an indefinitely extended projection of the Earth's axis of rotation intersects the celestial sphere. As the Earth rotates upon its axis, the north and south celestial poles remain permanently fixed in the sky (directly overhead to observers at the North Pole and South Pole, respectively), and all other points appear to rotate around them.

### cenote

    A natural pit or sinkhole resulting from the collapse of limestone bedrock which exposes groundwater underneath.

### census-designated place (CDP)

    A concentration of population identified by the United States Census Bureau for statistical purposes.

### central business district

    A centrally located commercial business district in an urban area, typically containing a concentration of office and retail activities.

### centroid

    The point in a geometric figure for which the coordinates are the average values of the coordinates of all other points in the figure, i.e. the arithmetic mean position of all points in the figure; or the point with the smallest possible average distance from all other points of the figure. In geography, the geographical center of a region of the Earth's surface is the centroid of the two-dimensional shape of that region, as projected radially to sea level or onto a geoid.

### chain

    A unit of length equal to 66 feet (20.117 m), used especially in public land surveys in the United States; 10 square chains is equal to 1 acre (0.40 hectares). Though the literal chains used to measure this distance have long been superseded, surveying tapes are often still called "chains", and measuring with a tape may be called "chaining".

### channel

    1. A waterway separating two relatively close landmasses.
    2. Any narrow body of water that connects two larger bodies of water.
    3. The deepest part of a shallow body of water, often used as a passageway for large ships.

### chaparral

    A class of terrestrial vegetation characterized by dense, impenetrable thickets of thorny shrubs or dwarf broadleaved trees, commonly found in northern Mexico and the southwestern United States.

### chart

    A special-purpose map designed for navigation, especially nautical and aeronautical navigation, or to present specific data or technical information.

### chimney

    See salient.

### chine

    A steep-sided coastal gorge, typically of soft eroding cliffs of sandstone or clay, through which a river or stream flows to the sea. The term is used primarily in southern England.

### chinook

    A warm, dry wind experienced along the eastern side of the Rocky Mountains in the United States and Canada. Most common in winter and spring, it can result in a rise in temperature of 20 °C (36 °F) in a quarter of an hour.

### chorography

    The art of establishing, describing, or mapping a geographic region or district, or more broadly, the representation of space or place.

### chorology

    The study of the causal relations of the phenomena present in a region; a comprehensive explanatory study of a region.

### choropleth

    A map showing the distribution of a phenomenon by graded shading which indicates the density per unit area of that phenomenon; the darker the shading, the greater the density.

### chott

    An ephemeral, often highly saline lake that forms seasonally with fluctuations in the water table, usually in the winter, in the desert basins of Northwest Africa.

### cinder cone

    A steep-sided volcano formed by the explosive eruption of cinders that form around a vent. Cinders are lava fragments about 1 centimetre (0.39 in) in diameter.

### circle of latitude

    See parallel.

### cirque

    An amphitheatre-shaped valley surrounded on three or more sides by steep, cliff-like slopes and formed by glacial or fluvial erosion.

### city

    A large human settlement, generally with extensive systems constructed for housing, transportation, sanitation, utilities, and communication.

### city-state

    A sovereign state or small independent country that usually consists of a single city and its dependent territories.

### clearing

    1. The practice of permanently removing vegetation, especially trees and bushes, from a forest or woodland in order to use the space for another purpose, such as agriculture, civic development, or paths for roads, railways, or power lines.
    2. Another name for a glade.

### cliff

    Any vertical or nearly vertical rock exposure, usually formed by the processes of weathering and erosion.

### cliffed coast

    A coastline where the repeated action of ocean waves has formed steep and often precipitous cliffs, as opposed to a flat or gently sloping alluvial coast.

### climax vegetation

    The vegetation that would exist in an area if growth had proceeded undisturbed for an extended period. This would be the "final" collection of plant types that presumably would remain forever, or until the stable conditions were somehow disturbed.

### clinometer

    See inclinometer.

### coast

    The area where land meets a sea or ocean. Coastal zones are regions where interactions between terrestrial and marine processes occur. Compare shore.

### coastal bench

    See wave-cut platform.

### col

    The lowest point on a mountain ridge between two peaks.

### colatitude

    The complementary angle of a given latitude; i.e. the arithmetic difference between 90 degrees and the given latitude. For example, the colatitude of 36° 22′ 49″ is 53° 37′ 11″.

### colony

    A territory under the immediate complete political control of a sovereign metropolitan state but otherwise distinct, often geographically, from the state's home territory. Colonies have no international representation independent of the metropolitan state. Compare satellite state.

### colluvium

    Loose, unconsolidated sediment that has been transported and deposited at the base of a hillslope by any of various wash or mass movement processes, such as surface runoff, sheet erosion, or landslides. Typically a heterogeneous mixture of rock types and sizes ranging from silt to talus boulders, colluvium is often derived from eluvium, and differs from alluvium, which is deposited primarily by fluvial activity.

### combe

    A steep, narrow valley or a large hollow on the side of a hill or coastline, especially one enclosed on all but one side. The term is used primarily in southern England, where it often implies a dry ravine in a limestone or chalk escarpment. See also cwm.

### compass

    An instrument used for navigation and orientation that indicates direction relative to the geographic cardinal directions by measuring the orientation of the Earth's magnetic field with respect to the North Magnetic Pole. Compasses often display markings for angles or degrees, which allow them to show azimuths and bearings, in addition to a compass rose.

### compass rose

    A figure on a compass, map, nautical chart, or monument used to display the orientation of the four cardinal directions — North, East, South, and West — and their intermediate points.

### compass survey

    A traverse which relies on the indications of a magnetic compass for orienting the traverse as a whole or for determining the directions of individual lines.

### confluence

    The place at which two or more rivers or other watercourses flow together to form one larger river or watercourse.

### coniferous

    Bearing cones; from the conifer family.

### contiguity

    The characteristic of a group of neighboring political or geographical divisions not being interrupted by politically unaffiliated land or water. Such divisions are said to be contiguous.

### continent

    One of several very large, contiguous landmasses into which the Earth's land area is divided, generally by geographical or political convention rather than any strict criteria. Geologically, continents correspond largely to areas of continental crust on continental plates.

### continental climate

    The type of climate found in the interior of the major continents in the middle or temperate latitudes. The climate is characterized by a great seasonal variation in temperatures, four distinct seasons, and a relatively small annual precipitation.

### continental divide

    The line of high ground that separates the different oceanic drainage basins of a particular continent. The river systems of a continent on opposite sides of a continental divide flow toward different oceans. See drainage divide.

### continental shelf

    A portion of a continent that is submerged beneath an area of relatively shallow water known as a shelf sea. Though continental shelves are usually treated as physiographic provinces of the ocean, they are not part of the deep ocean basin proper but the flooded margins of the continent.

### continentality

    The quality of being located on a continent.

### contour line

    A line marked on a topographic map which connects points of equal elevation above or below a specified reference datum. Multiple contour lines, each representing a different elevation, are depicted together to show the shape of the terrain within the map area.

### contour interval

    The difference in elevation between any two adjacent contour lines as depicted on a particular topographic map.

### conurbation

    An extensive urban area formed when two or more initially separate cities coalesce to form a continuous metropolitan area.

### cordillera

    A long chain of mountain ranges or highlands, especially those formed by the same orogeny and spanning the length of a continent along tectonic boundaries. The term is used in particular to refer to the American Cordillera, an almost continuous system of parallel ranges lining the west coasts of North, Central, and South America.

### core area

    The portion of a country or territory that contains its economic, political, intellectual, and cultural focus. It is often the center of creativity and change. See also hearth.

### cornice

    An accumulation of ice and wind-blown snow overhanging the edge of a ridge or cliff face, usually on the lee side of a steep mountain.

### corrasion

    The process of mechanical erosion of the Earth's surface by the impact or grinding action of particles being transported across it, either by moving water, waves, glaciers, wind, or gravity.

### corrie loch

    See tarn.

### cosmopolitan

    Occurring worldwide; belonging to all parts of the world and free of geographical or political limitations. See also global.

### coulee

    A dry canyon eroded by Pleistocene floods that cut into the lava beds of the Columbia Plateau in the western United States.

### couloir

    A narrow gully with a steep gradient in a mountainous terrain, often enclosed by sheer cliffs and filled with snow or ice even during the summer months.

### country

    A region identified as a distinct national entity in political geography. Compare state.

### county

    A type of subnational division of a country or federal state used for administrative or other purposes.

### course

    The cardinal direction in which a vessel or aircraft is moving, or in which it is steered. This is not necessarily the same as the heading, the direction in which the craft's bow or nose is pointed; any difference between heading and course is due to the motion of the air or water through which the vessel is moving, or other aerodynamic effects such as skidding or slipping. See also bearing.

### cove

    1. A walled, rounded, cirque-like opening at the head of a small valley.
    2. A small, narrow, sheltered bay, inlet, tidal creek, or recess in an estuary, often within a larger embayment.
    3. A small, often approximately circular, wave-cut indentation or recess in a cliff on a large body of water, especially one with a relatively narrow or secluded entrance.
    4. A shallow tidal river, or the backwater near the mouth of a tidal river.

### crater

    Any large, roughly circular depression, pit, or hole in the Earth's surface. Craters can be classified into different types based on their ultimate causes; see impact crater, volcanic crater, and pit crater.

### crater lake

    A lake that forms in a volcanic crater or caldera (such as a maar), an impact crater left by a meteorite, or a crater resulting from a man-made explosion.

### craton

    An old and stable region of continental lithosphere, characterized by a thick crust composed of ancient crystalline basement rock. Cratons are generally found in the interiors of tectonic plates, having remained relatively unaffected by orogenic and tectonic activity for very long periods of time.

### creek

    A small, intermittent stream that is larger than a brook but smaller than a river. The term is used primarily in the United States, Canada, and Australia.

### crevasse

    1. A deep crack, fissure, or chasm in the ice of a glacier or ice sheet, or more generally in any ground surface.
    2. A break in the natural levee or bank of a river.

### crust

    The thin shell of solid material that is the Earth's outermost layer and the outermost component of the lithosphere. The Earth's crust is generally divided into two distinct types, oceanic crust and continental crust, both of which "float" on top of the mantle.

### cryosphere

    The totality of water in the solid phase on the Earth's surface, including glaciers; sea, lake, and river ice; snow; and permafrost. The cryosphere is sometimes considered a subset of the hydrosphere.

### cryoturbation

    The mixing of materials from various horizons of the soil down to the bedrock due to freezing and thawing.

### cuesta

    A long, low ridge with a steep scarp slope and a gentle backslope (dip slope).

### cultural geography

    A branch of human geography which studies the patterns and interactions of human culture in relation to the natural environment and the human organization of space.

### culture

    The accumulated habits, attitudes, and beliefs of a group of people that define for them their general behavior and way of life; the total set of learned activities of a people.

### culture hearth

    The area from which the culture of a group diffused. See also hearth.

### culvert

    A tunnel or conduit that channels water through or beneath an obstacle (e.g. through a man-made crossing of a ravine that would otherwise block the natural flow of water), or any artificially buried watercourse.

### curvimeter

    See opisometer.

### cusp

    An arc-shaped, dune-like mound of sediment on a beach or foreshore. Cusps tend to be uniformly spaced in repeating patterns close to the shoreline, with the embayment of each arc made of fine-grained sand or gravel and the "horns" made of coarser sediment.

### cut bank

    A continually eroding bank along a meandering river or stream channel, especially a bank that has been eroded into a nearly vertical cliff. Cut banks generally form on the outside bend of a deep meander, opposite the depositional point bar that forms on the inside bend.

### cutoff

    The new channel formed when a meandering stream erodes through a narrow strip of land and thereby shortens the length of the main channel.

### cwm

    See cirque.

### Cyclopean stairs

    A term referring to the longitudinal profile of some glaciated valleys which have been eroded into a series of consecutive hanging valleys resembling stairs.
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## D

### dale

    Another name for a valley.

### dam

    Any barrier, either natural or artificial, that stops or restricts the flow of water, either on the surface or underground. Man-made dams are most commonly built to impound rivers or streams, generally to retain water for purposes such as human consumption, irrigation, aquaculture, or power generation (whereas related structures such as floodgates and levees are more specifically designed to manage or prevent water flow into particular areas).

### dasymetric map

    A type of thematic map that uses areal symbols to visualize a spatially dependent variable (e.g. population density) by refining a choropleth map with ancillary information about the distribution of the variable. The dasymetric method attempts to improve the resolution of maps based on average or per-capita figures calculated for discrete administrative units, which tend to show sharp contrasts between adjacent areas, by supplementing these figures with additional geographic data that allow more precise categories to be constructed. Dasymetric maps are a hybrid of choropleth and isarithmic maps, combining their strengths and weaknesses in order to more accurately depict quantities that vary continuously across space.

### datum plane

    The zero-elevation baseline or vertical datum to which a measurement of elevation or altitude is relative, e.g. the mean sea level calculated for a given location over a given period of time. See also geodetic datum.

### de facto segregation

    The spatial and social separation of populations that occurs without legal sanction.

### de jure segregation

    The spatial and social separation of populations that occurs because of legal measures.

### debouch

    A place where water runoff from a relatively small, confined space emerges into a much larger, broader space, or where a body of water pours forth from a narrow opening, such as where a stream or river enters a lake or ocean.

### deciduous forest

    A forest composed of trees which lose their leaves each year.

### deep

    A trough-like depression or trench in the ocean floor, of limited extent but great depth, generally more than 5,500 metres (18,000 ft) below sea level.

### defile

    A narrow pass or gorge between mountains or hills.

### degree

    A unit of angular measure, represented by the º symbol. A circle is divided into 360 degrees; subdivisions of the degree include the minute (1⁄60 of one degree) and the second (1⁄3600 of one degree). Degrees are commonly used to divide the roughly spherical shape of the Earth for geographic and cartographic purposes, e.g. when reporting latitudes and longitudes.

### degree day

    Deviation of one-degree temperature for one day from an arbitrary standard, usually the long-term average temperature for a place.

### dell

    A small, secluded hollow, usually within a grassy, park-like, partially wooded valley.

### delta

    A landform at the mouth of a river where the main stem splits up into several distributaries. It is formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river. Compare estuary.

### demography

    The study and systematic analysis of population, particularly human population.

### demoiselle

    A pillar of rock weathered from volcanic breccia or similar material and capped by a large boulder which has protected the material underneath.

### denudation

    The uncovering of deeper layers of rock by any natural process, e.g. erosion, weathering, or mass movement.

### dependency

    A territory relying on or subject to the control of another country, neither possessing full political independence nor forming an integral part of the controlling country's political or economic interests.

### deposition

    Any natural process by which material such as soil and rocks is added to a landform or landmass, e.g. by the action of wind, water, ice, or gravity in transporting previously weathered surface material, which comes to rest when sufficient kinetic energy is lost and accumulates in layers of sediment. See also sedimentation.

### depression

    Any landform that is sunken or depressed below the surrounding area. Depressions include an enormous variety of landforms and can form by a number of different mechanisms, including erosion, ground collapse, tectonic activity, volcanism, and meteorite impacts.

### derelict land

    An area of land which has been damaged or devalued by some process, either natural or man-made (e.g. extractive industry), and/or simply neglected, causing it to be abandoned by human interests (and often other organisms) and leaving it incapable of being used productively in its present condition. See also brownfield land.

### desert

    An arid, barren area of land where little precipitation occurs and living conditions are consequently unfavorable for most plant and animal life. Deserts are characterized by exposure of the unprotected ground surface to processes of denudation as well as large variations in temperature between night and day. They are often classified by the amount of precipitation they receive, by their average temperature, by the causes of their desertification, or by their geographical location.

### desert pavement

    A ground surface, often found in arid environments, covered with interlocking rock fragments of pebble and cobble size, closely packed after the removal of finer rock material and smoothed or polished by blown sand so that eventually their upper surfaces are more or less uniformly flat.

### desert varnish

    A conspicuous orange-yellow to black coating often present on exposed rock surfaces in arid environments, consisting of thin, hard, polished layers of metal oxides, especially iron and manganese, which form when minute quantities of matter migrate to the surface of the rock by capillary action and are then precipitated by evaporation.

### desertification

    The process by which a previously fertile area becomes increasingly arid, infertile, or desert-like; a type of land degradation in which biological productivity is lost due either to natural or man-made processes, e.g. climate change or overexploitation of soils for agriculture.

### desire line

    A straight line drawn on a map between the point of origin and the destination of a trip, i.e. the shortest distance between these two points, indicating the route a person would like or desire to follow if it were possible.

### desire path

    Any path or trail, often a footpath, created as a consequence of erosion caused by human or animal traffic, usually representing the shortest or easiest route to navigate between an origin and a destination. Desire paths often emerge as shortcuts where constructed paths or roads are circuitous, have gaps, or are non-existent.

### dew pond

    A shallow artificial pond built to capture and hold rainwater or sea mist in order to water livestock, made especially in areas where natural supplies of surface water are not readily available, such as on the chalk downlands of southern England.

### diaspora

    The scattered dispersion of a human population from its original homeland; or the members of a dispersed population, now residing in various locations to which they are not indigenous.

### digital elevation model (DEM)

    A three-dimensional computer graphics representation of a geographic terrain surface created from elevation data. DEMs are the most common basis for digitally produced relief maps.

### dike

    1. A ditch, wall, embankment, or ridge, natural or man-made, that is an obstacle to something else; another name for a levee.
    2. In geology, an intrusion in which molten rock has ascended through an approximately vertical fissure and solidified into a wall of rock that is often harder or less permeable than the rocks of the surrounding strata.

### diocese

    A type of administrative division used by certain Christian churches for religious purposes.

### discharge

    In hydrology, the volumetric flow rate of water through a particular cross-sectional area, i.e. the volume of water that passes a particular point along a waterway (e.g. a cross-section of a stream channel) per unit time. The measure includes the volumes of any suspended solids, dissolved chemicals, or organic matter in addition to the water itself. Discharge is commonly measured for both natural and man-made hydrological systems, where it may be referred to by various names including streamflow and outflow.

### discordant coastline

    A coastline which cuts transversely across the predominant orientation of the local geological strata, i.e. not parallel to them, as with a concordant coastline.

### dissected plateau

    A landscape produced by significant stream erosion and incision of a plateau such that only a small part of the plateau surface is at or near the original elevation of the summit; much of the area instead occurs as eroded hills or badlands.

### distance decay

    The decrease in cultural or spatial interactions between two places as the distance between them increases. This effect may be noticeable in towns and cities, where certain characteristics such as pedestrian traffic, building height, and land value tend to decline with greater distance from the city center.

### distributary

    A stream or river that branches off and flows away from a main channel and does not return to it. Distributaries are common near river deltas. Contrast tributary.

### district

    A type of administrative subdivision used by governments and institutions worldwide, typically at regional or local levels. Districts are commonly drawn to define the jurisdictions of special local government services, such as law enforcement and education, and often function more or less independently of the municipal or county governments that designate them. The term can refer to a wide variety of official and colloquial subdivisions, including electoral districts, school districts, and shopping districts.

### divide

    See drainage divide.

### doab

    In parts of South Asia, the low alluvial plain lying between and reaching to the confluence of two rivers or streams. See also interfluve.

### doline

    A shallow enclosed basin or funnel-shaped depression typical of karst landscapes, usually with a flat floor and linked to the underlying drainage system by a vertical shaft. See also sinkhole.

### dome

    1. A steep-sided mound that forms when very viscous lava is extruded from a volcanic vent.
    2. An uplifted area of sedimentary rock with a downward dip in all directions, often caused by molten rock material pushing upward from below. The sediments have often eroded away, exposing the rocks that resulted when the molten material cooled.

### donga

    In southern Africa, another name for a gully or badland carved by extreme erosion.

### dormant volcano

    An active volcano that is in repose (quiescence) but is expected to erupt in the future.

### dormitory town

    See commuter town.

### downland

    An open, treeless expanse of gently undulating, elevated grassland, usually of chalk and supporting grazing for livestock. The term is used primarily in southern England, Australia, and New Zealand.

### downtown

    In English-speaking North America, the commercial, cultural, and often historical and/or geographical center of a city or town, especially a large city within a major metropolitan area, often synonymous with its central business district.

### drainage

    The natural or artificial removal of surface and/or sub-surface water from an area with excess water, e.g. via runoff facilitated by channels such as streams and rivers, into which water collects and is transported to sea level by gravity. The patterns, hierarchies, and evolution of drainage networks are widely studied in physical geography disciplines.

### drainage basin

    Any area of land where precipitation collects and drains into a common outlet, such as into a river, lake, ocean, or any other body of water. The drainage system includes all of the surface water from precipitation runoff and snowmelt, as well as all of the groundwater beneath the Earth's surface. Each drainage basin is separated topographically from adjacent basins by a drainage divide.

### drainage divide

    The topographical barrier that separates neighboring drainage basins. Divides are often, though not always, located along conspicuous elevated ridges or mountain ranges.

### draw

    1. A terrain feature formed by two parallel ridges or spurs with low ground in between them.
    2. Another name for an arroyo, ravine, or gulch, especially one with a broad floor and gently sloping sides.

### draw down

    The maximum extent to which the water table is reduced in elevation as a result of pumping water from a well that penetrates an aquifer. The amount of draw down diminishes logarithmically with distance from the site of the well, a fact which determines the shape of the subsurface cone of depression in the area surrounding the well.

### drift ice

    A type of sea ice consisting of multiple ice floes that are not attached to the shoreline or any other fixed object such as a shoal, and which are therefore free to "drift" under the influence of winds and ocean currents. Contrast fast ice.

### drowned valley

    A valley which was originally formed on land but later partially or entirely submerged beneath the sea due to a rise in sea level. See also fjord, calanque, and ria.

### drumlin

    An elongated hill in the shape of an inverted spoon or half-buried egg which is formed by glacial ice acting on underlying unconsolidated till or ground moraine.

### dry farming

    A type of farming practiced in semi-arid or dry grassland areas without irrigation, instead using such approaches as fallowing, maintaining a finely broken surface, and growing drought-tolerant crops.

### dry gap

    See wind gap.

### dry point

    An area of firm or dry ground in a wetland, marsh, or floodplain, often capable of supporting a human settlement.

### dryland

    An ecoregion or more generally any land area defined by a relative scarcity of water, where precipitation is evenly balanced or exceeded by evaporation from surfaces and evapotranspiration by plants. Drylands encompass all sub-humid and arid environments, from tropical savannas to hyper-arid extremes such as deserts.

### dune

    A hill of loose sand built by the movements and erosional and depositional processes of wind or water, often occurring in deserts and coastal areas.
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## E

### Earth science

    1. A collective term for the various fields of natural science related to the planet Earth.
    2. The branch of science that studies the physical constitution and characteristics of the Earth and its atmosphere, using methods and tools from geography, geology, physics, chemistry, biology, and mathematics to build a quantitative understanding of how the Earth works and changes over time.

### earthquake

    A sudden and intense shaking of the ground due to tectonic activity.

### Eastern Hemisphere

    The half sphere of the Earth that is east of the Prime Meridian and west of the antimeridian. It is opposite the Western Hemisphere.

### economic distance

    The physical distance a commodity may travel before its value is exceeded by the costs of transporting it.

### economic geography

    A sub-discipline of geography which studies the location, distribution, and spatial organization of economic activities across the world.

### economies of agglomeration

    The economic advantages that accrue to an activity by locating close to other activities; benefits that follow from complementarity or shared public services.

### ecoregion

    A type of biogeographic province that is smaller than a bioregion and which contains characteristic, ecologically and geographically distinct, and relatively uniform assemblages of biological communities and species. Ecoregion boundaries often overlap within ecotones and mosaic habitats, and most ecoregions contain habitats that differ from those described for their assigned biome.

### ecotone

    A transition area between two biological communities, where different communities meet and integrate. It may manifest as a gradual blending of the communities across a broad area, or as an abrupt boundary line.

### ecumene

    1. The habitable world according to the ancient Greeks; the part of the Earth's surface that is suitable for permanent human settlement, e.g. because it is climatically tolerable and physically occupiable.
    2. All of human civilization considered collectively.

### edge city

    A concentration of businesses, commercial buildings, or retail and entertainment venues situated outside of a traditional downtown or central business district in what was previously a suburban residential or rural area.

### edgelands

    The transitional areas of "fringe" space at the boundaries of a country, city, or other artificial geographical entity, often distinguished by a partly man-made, partly natural landscape that is in the earliest stages of human management and organization. Compare hinterland.

### effective accessibility

    The extent to which a place or service is actually accessible, governed not only by the distance to be traveled but also by whether or not the means of transport, the time available, and social circumstances make access possible.

### ekistics

    The scientific study of human settlements of all types, incorporating concepts such as regional, metropolitan, and community planning and dwelling design with the goal of achieving harmony between the inhabitants of a settlement and their physical, social, and cultural environments.

### electoral geography

    A branch of human geography concerned with analysis of the organization, methods, results, and consequences of political elections in the context of geographic space and using geographical techniques.

### elevation

    1. The height of a geographic location above or below a fixed reference point; in particular, the height of a point on the Earth's surface with respect to sea level (or at least to a reference geoid used as an approximation of the Earth's mean sea level). Compare altitude, geopotential height, and depth.
    2. The vertical angle between the horizontal and a high point, e.g. between the horizon and a star in the night sky, or between the base of a mountain and its summit.
    3. In architecture, a view of one of the sides of a building, or a drawing of this view.

### ellipsoid

    See reference ellipsoid.

### emergence

    1. The rise of the level of a land surface with respect to the sea, so that land formerly under the sea becomes dry.
    2. The location at which an underground stream or aquifer comes to the surface.

### emergent coastline

    A coast or shoreline resulting from a rise in land surface elevation relative to sea level.

### empolder

    To reclaim by the creation of a polder.

### enclave

    A tract or territory completely surrounded by and enclosed within the territory of exactly one other state, country, or other political entity. Unlike enclaves, exclaves can be surrounded by more than one other state.

### endemic

    Restricted or exclusive to a certain place, region, or people, having originated there, and existing nowhere else.

### endorheic basin

    A closed drainage basin that allows little or no outflow to external bodies of water but converges instead into internal lakes or swamps which equilibrate through evaporation.

### englacial

    Embedded within a glacier. Contrast subglacial and superglacial.

### entrepôt

    A place (e.g. a port, city, or trading post) to which physical goods or merchandise are brought to be stored temporarily while awaiting export to another country, and where they are not liable to customs duties. Though the term once described important commercial centers situated along long-distance trade routes, modern customs areas have largely made such entrepôts obsolete, and the term is now more commonly used to refer to duty-free ports with a high volume of re-export trade.

### environs

    The area surrounding a particular geographical place, i.e. its surroundings or environment.

### epeiric sea

    A large, shallow body of saltwater on a continental shelf which is connected to the ocean; an inland sea. See also marginal sea.

### epicenter

    The point on the Earth's surface directly above the focus of an earthquake, near which the seismic waves produced by the earthquake are usually most noticeable.

### Equator

    The imaginary great circle around the Earth halfway between the geographic poles which is assigned a latitude of zero degrees and therefore used as a reference point for all other lines of latitude. It is the largest circumference of the Earth.

### erg

    A broad, flat desert area covered by wind-swept sand and having little or no vegetative cover.

### erratic

    A boulder that has been carried from its source by a glacier and deposited as the glacier melted. Such boulders are often conspicuous because they differ geologically from the surrounding rock.

### escarpment

    A long cliff or steep slope separating two comparatively level or more gently sloping surfaces and resulting from erosion or faulting.

### esker

    A long, winding ridge of stratified sand and gravel, usually occurring in glaciated or formerly glaciated areas.

### estavelle

    A karstic sinkhole or ponor which, depending on the season and weather conditions, can serve as either a sink or a source of freshwater.

### estuary

    The broad lower course of a river where it enters the ocean and is affected by the tides. Compare delta.

### étang

    A shallow pool or lake caused by the ponding of backwash draining from a beach by material brought ashore by the sea.

### etchplain

    A plain beneath which the bedrock has been subjected to considerable subsurface weathering, known as "etching". Erosion of the regolith overlying an etchplain often exposes topographical irregularities such as inselbergs.

### evorsion

    See pothole.

### exaration

    See plucking.

### exclave

    A portion of a state or territory that is geographically separated from the main part by surrounding foreign territory of one or more other states or political entities. Many exclaves are also enclaves.

### exotic stream

    A stream found in an area that is too dry to have spawned such a flow. The flow originates in some moister section.

### extinct volcano

    A volcano that is not expected to erupt again.

### exurban

    An adjective describing a region or district that lies outside a city and usually beyond its suburbs; a place of this type is called an exurb. Compare rural.
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## F

### fairway

    The part of a navigable waterway containing the navigable channel, in particular the central, deepest, widest, or most commonly used channel.

### fall line

    A geomorphologic unconformity between an upland region of relatively hard crystalline basement rock and a coastal plain of softer sedimentary rock.

### fallow

    Agricultural land that is plowed or tilled but left unseeded during a growing season. Fallowing is usually done to conserve moisture and soil nutrients.

### false origin

    A selected point in a projected coordinate system from which the position of any place can be expressed in terms of its coordinates with respect to the selected point. The false origin differs from the true origin in order to exclude negative values.

### fault

    A fracture in the Earth's crust accompanied by a displacement of one side of the fracture.

### fault-block mountain

    A mountain mass created by either the uplift of land between faults or the subsidence of land outside the faults.

### fault zone

    An area of numerous fractures in the Earth's crust along which movement has occurred. The movement may be in any direction and involve material on either or both sides of the fractures.

### federation

    A form of government in which powers and functions are divided between a central government and a number of political subdivisions that have a significant degree of political autonomy.

### felsenmeer

    See blockfield.

### fen

    An area of spongy, waterlogged ground containing decaying vegetation that accumulates over time into peat, and which is supplied with an input of mineral-rich surface or groundwater and thereby directly connected to a larger hydrological system. This external input typically results in higher mineral concentrations and a more alkaline pH than other peat-forming ecosystems such as bogs. Fens are one of four main types of wetland, along with bogs, marshes and swamps.

### field

    1. Any large, open outdoor space, natural or man-made, especially one with a natural surface covering such as grass or soil and having few trees and structures, permitting long sightlines.
    2. (variable) A property, quantity, or observation (e.g. temperature, soil moisture, population density, etc.) that can be theoretically assigned to any point of space and which varies across space. Both scalar and vector fields are found in GIS applications, although the former is more common. Also spatially dependent variable.

### figure of the Earth

    The size and shape of the Earth as studied in geodesy. Applications requiring varying levels of precision have led to the development of many different models of the Earth, ranging from simple spheres to much more accurate approximations such as geoids.

### firn

    A type of ice that is at an intermediate stage between snow and glacial ice. More specifically, firn is partially compacted névé left over from past seasons which has subsequently recrystallized into a form that is harder and denser than névé.

### first bottom

    A colloquial term loosely applied to the topographically lowest step of a floodplain that experiences regular flooding, i.e. the first part to be inundated when a flood occurs (though the frequency considered "regular" is inconsistently specified). The term is used primarily in the Midwestern United States.

### First Law of Geography

    A fundamental assumption of spatial analysis articulated by the Swiss-American geographer Waldo Tobler as "Everything is related to everything else, but near things are more related than distant things." This principle is considered foundational to the concepts of spatial dependence and autocorrelation, and is expressed mathematically in the inverse distance weighting method of spatial interpolation and in regionalized variable theory as the basis for kriging.

### firth

    Another name for a coastal inlet, strait, or bay associated with the mouth of a large river, where the tidal effects of seawater passing upriver have widened the riverbed into an estuary. The term is used primarily in Scotland.

### fish ladder

    A series of shallow steps down which water is allowed to flow, designed to permit salmon or other anadromous fish to circumvent artificial barriers such as dams as they swim upstream to spawn.

### fissure

    A long, narrow opening or line of breakage made by cracking or splitting, especially in rock or earth.

### fjard

    A large, open, navigable body of water between the islands of an archipelago or between an island and the mainland, either on the sea coast or in freshwater lakes or rivers.

### fjord

    A long, narrow, navigable marine inlet with steep sides or cliffs created by glacial erosion.

### flood wall

    A primarily vertical artificial barrier designed to temporarily contain the waters of a river or other waterway which may rise to high levels during flooding events. Flood walls are narrower and typically easier to build than dikes or levees, so they are mainly used in locations where space is limited or where building more traditional flood-control structures would interfere with other interests.

### floodbank

    See levee.

### floodplain

    A broad, flat area of land adjacent to a river or stream which is leveled by annual flooding and by the lateral and downstream movement of meanders.

### floodway

    1. Another name for a flood bypass.
    2. A large-capacity channel or culvert designed to capture and divert floodwaters or excess streamflow from populous or flood-prone areas and eventually drain it into a river or other body of water, e.g. an artificial drainage canal bounded by levees. They often run below street level in larger cities.
    3. A road crossing of a flood-prone channel, built at or close to the natural ground level. It is similar to a causeway but crosses a shallow and often dry depression that is subject to flooding, rather than a continuously flooded waterway.
    4. A part of a floodplain kept clear of encumbrances and reserved for emergency diversion of floodwaters.

### floor

    The level or nearly level lower part of a valley or basin, or the bed of any body of water, such as a stream, lake, or ocean.

### flute

    A glacial landform created by the movement of a glacier around a boulder, consisting of a lineation or streamlined furrow or ridge parallel to the direction of ice movement. They generally form in newly deposited till or older drift and can reach heights of 25 metres (82 ft) and lengths of 20 kilometres (12 mi).

### fluvial

    Of or pertaining to rivers or streams; produced by the action of a river or stream.

### focality

    The characteristic of a place that follows from its interconnections with more than one other place. When interaction within a region comes together at a single place (i.e. when the movement focuses on that location), the place is said to possess focality.

### focus

    The point inside the Earth's crust from which an earthquake originates.

### foothills

    A geographic transition zone defined by gradual increases in elevation between plains or low-relief hills and adjacent topographically higher hills, mountains, or uplands.

### footslope

    The part of the profile of a hillslope that forms the concave surface at the base of the slope. It is a transition area between sites of erosion and transport higher up the slope (e.g. the shoulder and backslope) and sites of deposition further down the slope (the toeslope).

### ford

    A place, natural or man-made, where a river or stream is shallow enough to be crossed by wading, or by getting a vehicle's wheels wet (as opposed to crossing a permanently dry bridge). Fords may be seasonal or temporary, becoming impassable during high water.

### foredeep

    A relatively narrow, deep, elongated, and steep-sided trough in the ocean floor, usually near or parallel to a mountainous land area or associated with an archipelago, or such a trough when infilled with sediment. See also foreland basin.

### foreland

    1. Any land area or territory located in front of something else.
    2. A landform projecting into the sea, e.g. a cape or headland.
    3. The seaward trading area associated with a particular port or harbor.
    4. (glaciology) The area between the current leading edge of a glacier and the moraines of the most recent maximum.

### foreland basin

    A type of structural endmember basin that develops adjacent and parallel to a mountain range as a result of lithospheric flexure during its orogeny. Topographic loading and downflexure creates space in the basin that is filled by sediment eroded from the range. Compare rift basin.

### foreshore

    The part of a seashore located between the lowest low water line and the mean high water line. See also intertidal zone; contrast backshore.

### forest

    Any extensive area dominated by communities of trees.

### form line

    A contour line whose precise position on a map has not been accurately surveyed but rather interpolated from surrounding contours.

### fresh water

    Any naturally occurring water characterized by low concentrations (typically less than 0.05% by volume) of dissolved salts and other solids relative to either salt water or brackish water. Sources of fresh water on Earth include glaciers, ice caps, icebergs, bogs, lakes, rivers, streams, and most groundwater.

### functional diversity

    The characteristic of a place where a variety of different activities (economic, political, or social) occur, most often associated with urban places.
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## G

### gazetteer

    A geographical dictionary or directory used in conjunction with a map or atlas and containing information concerning the geographical make-up, social statistics, and physical features of a country, region, or continent.

### geodesy

    The science of accurately measuring and understanding the Earth's geometric shape, orientation in space, and gravitational field and how these properties change over time.

### geodetic datum

    A coordinate system and set of reference points used for locating places on the Earth, which defines horizontal and vertical coordinates upon a particular reference ellipsoid that approximates the figure of the Earth. Geodetic datums are used in geodesy, navigation, and surveying applications to translate positions indicated on paper or digital maps to their actual positions on the Earth; because the Earth is an imperfect ellipsoid, localized datums such as the ED50 covering only specific countries or regions are often more accurate representations of their area of coverage than global standards such as the WGS 84 of the World Geodetic System.

### geodetic north

    See true north.

### geodetics

    See geodesy.

### geodynamics

    A subfield of geophysics and Earth science that studies the physical dynamics of the Earth by applying physics, chemistry, and mathematics to the understanding of how mantle convection and other internal processes lead to plate tectonics and geological phenomena such as mountain formation, volcanism, earthquakes, and faulting, among others.

### geographic coordinate system

    A coordinate system used in geography that enables every location on Earth to be specified by a set of numbers, letters, or symbols. Geographic coordinates are often chosen such that one of the numbers represents a vertical position such as elevation and two or three other numbers represent a horizontal position such as latitude and longitude.

### geographic information science (GIS)

    The scientific study of data structures and computational techniques for capturing, representing, processing, and analyzing geographic information.

### geographic information system (GIS)

    Any system of computer software tools designed to allow users to record, store, manipulate, analyze, manage, and present large sets of spatial or geographic data.

### Geographic Names Information System (GNIS)

    A digital public-domain database developed by the U.S. Geological Survey and the U.S. Board on Geographic Names which contains name and locative information about more than two million physical and cultural features located throughout the United States and its territories. Each feature recorded in the database receives a unique feature record identifier called a GNIS identifier.

### geographical inertia

    The tendency of a place with established installations and services to maintain its size and its importance as a focus of economic or industrial activity after the conditions originally influencing its development have appreciably altered, ceased to be relevant, or disappeared.

### geographical mile

    A unit of length defined as the distance equal to one minute of arc along the Earth's Equator: approximately 1,855.3 metres (1.1528 mi; 1.8553 km). The precise length varies with the reference ellipsoid used to approximate the shape of the Earth. Regardless of the particular ellipsoid, the length of one degree of longitude at the Equator is equal to exactly 60 geographical miles.

### geography

    The scientific study of the lands, features, inhabitants, and phenomena of Earth.

### geoid

    The shape that the surface of the Earth's oceans would take under the influence of Earth's gravity and rotational acceleration alone, in the absence of other influences such as winds and tides. It is often characterized as the precise mathematical figure of the Earth: a smooth but irregular gravitational equipotential surface at every point of which, by definition, the direction of the force of gravity is always perpendicular and spirit levels are always parallel. Its shape results from anomalies in the Earth's gravitational field caused by the uneven distribution of mass within and on the Earth's surface. A reference ellipsoid is an idealized approximation of the more complex and accurate geoid.

### geoinformatics

    The science and technology which develops and uses information science infrastructures to address problems and analyze data within geography, cartography, geoscience, and related branches of science and engineering.

### geolocation

    The identification or estimation of the real-world geographic location of an object, involving the generation of a set of geographic coordinates in order to determine a more meaningful description of location, such as a street address.

### geomatics

    The scientific discipline that involves gathering, storing, processing, and delivering geographic or spatially referenced information.

### geomorphology

    The study of the arrangement and form of the Earth's crust and of the relationship between these physical features and the geologic structures beneath.

### geoscience

    See Earth science.

### geosophy

    The study of geographical knowledge from any and all points of view, past or present, true or false; the study of the nature and expression of geographical ideas.

### geospatial science

    See geomatics.

### geosphere

    The collective non-living parts of the Earth: the lithosphere, the atmosphere, the cryosphere, and the hydrosphere.

### geostatistics

    A branch of statistics which involves the organization, management, and analysis of spatial and spatiotemporal datasets. Geostatistical algorithms are often incorporated in GIS software applications.

### geosystems

    See physical geography.

### ghetto

    A section of a city occupied by members of a minority group who live there because of social restrictions on their residential choices. Originally, the term referred specifically to a section of a European city to which Jews were confined.

### ghost town

    A deserted or abandoned village, town, or city, especially one in which remaining buildings and infrastructure such as roads are still visible. The term is also sometimes used to refer to settlements that are still populated, but significantly less so than in previous years.

### glacial

    Of or pertaining to a glacier or to the consequences of glaciation; formed, deposited, caused, or affected by glaciological processes.

### glacial drift

    See drift.

### glacial flour

    See rock flour.

### glacial lake

    A lake or other enclosed body of water created by historical or ongoing glacial activity; e.g. the Great Lakes of North America.

### glacial till

    The mass of rocks and finely ground material carried by a glacier and deposited when the ice melts. This creates an unstratified material of varying composition.

### glaciation

    1. The process or state of being covered with a glacier.
    2. Another name for a glacial period, an interval of time that is marked by colder temperatures and advancing glaciers.

### glacier

    A persistent mass of dense ice that is constantly moving under its own weight, and which is composed largely of compacted snow that forms where the annual accumulation of snow exceeds its melting and sublimation over very long periods of time. Glaciers slowly deform and abrade the land beneath them, creating a huge variety of landforms including cirques, moraines, and fjords. They form exclusively on land and are distinct from the much thinner ice that forms on bodies of water.

### glaciology

    The scientific study of glaciers, including their formation, composition, behavior, causes, effects, and distribution; or more generally of ice or any natural phenomena involving ice.

### glacis

    A smooth, gently sloping surface at the foot of a hill, mountain, or any other high promontory, whether natural or artificial. In the latter case, the term is used in particular to describe a stone or earthen slope constructed at the base of some historical military fortifications.

### glade

    Any large, open, mostly treeless area within a forest.

### glen

    A long valley bounded by gently sloping, concave sides, and typically narrower and deeper than a strath. The term is used primarily in Scotland.

### glint

    A steep cliff, terrace, or edge of a plateau.

### global

    1. Of or concerning all parts of the world (i.e. worldwide); affecting or distributed across the whole of the Earth.
    2. Of or relating to a globe or sphere; spherical.
    3. Comprehensive; total; encompassing all or nearly all considerations, categories, items, etc.

### global city

    A city which functions as an important or primary node in the global economy. Though criteria are not strictly defined, a global city typically is very large; dominates trade and economic interactions within a large surrounding area; supports a large and demographically diverse population; serves as a center of ideas and innovation in business, science, culture, and politics; and/or is a headquarters for major financial institutions, multinational corporations, or worldwide media and communications networks.

### Global Positioning System (GPS)

    A satellite-based radionavigation positioning system owned and operated by the United States Department of Defense and made available for use by both the military and the general public. It is one of several GNSS standards that provides geolocation and time information, transmitted via microwave signals, to enabled satellite navigation devices, known as GPS receivers, anywhere on or near the Earth where there is an unobstructed line of sight to at least four GPS satellites. Modern state-of-the-art GPS receivers can accurately pinpoint locations to within 30 centimetres (0.98 ft).

### globalization

    The process of interaction and integration among people, companies, governments, and cultures across the world. A complex and multifaceted phenomenon, globalization is considered largely the result of economically motivated advances in transportation and communication technologies in the past several centuries which have dramatically increased interactions between otherwise isolated groups of people.

### globe

    A true-to-scale map of the Earth that duplicates its round shape and correctly represents relative areas, sizes, and shapes of physical features, distances, and directions.

### gnamma

    See panhole.

### gore

    1. An irregularly shaped parcel of land of any size, often approximately triangular, that is left between two adjoining surveyed parcels as the result of incomplete or inaccurate boundary surveys.
    2. A lune-shaped map which may be fitted to the surface of a globe with a negligible amount of distortion.

### gorge

    See canyon.

### graben

    A depression or valley bounded on either side by distinct, parallel escarpments or faults and formed by the downward displacement of a block of the Earth's crust. Grabens often occur side-by-side with horsts, their uplifted or non-displaced counterparts, in a repeated series of vertical displacements.

### grade

    A physical surface that is inclined with respect to the horizontal, or the angle between that surface and the horizontal, typically expressed in degrees, or calculated as a ratio of "rise" (vertical distance) to "run" (horizontal distance) and expressed as a fraction or percentage; a larger number indicates a steeper incline. The term "grade" is often used to describe the incline of man-made surfaces such as roads and the roofs of buildings, whereas the term "slope" is more commonly used to describe natural surfaces such as the sides of hills or mountains or the beds and banks of watercourses.

### grassland

    Any land area where the vegetation is dominated by grasses (i.e. plants of the botanical family Poaceae), sometimes also inclusive of grass-like plants of other families. A large and important biome occurring worldwide, grasslands may be natural or created for agricultural purposes.

### graticule

    A network of lines on a map or chart (or imagined on the surface of the Earth) representing geodetic parallels of latitude and meridians of longitude.

### gravimetry

    The measurement of the strength of a gravitational field, especially the Earth's gravitational field, typically by calculating the acceleration due to gravity at a particular point on the Earth's surface. Because it can vary widely across the surface, knowing the local magnitude of the gravitational force is often necessary in order to produce accurate geographical data.

### great circle

    Any circle on the surface of a sphere created by the intersection of the sphere and a plane that passes through its center. A great circle divides the sphere into two equal hemispheres, and all of a sphere's great circles have the same center and circumference as each other, which by definition is the largest possible circumference of the sphere. The mathematical properties of great circles make them useful in geodesy, where they are often visualized upon the surface of the Earth (despite the fact that the Earth is not a perfect sphere): for example, the Equator of the idealized Earth is a great circle, and any meridian with its antimeridian forms a great circle. Because the shortest path between any two points on the surface of a sphere follows the arc of a great circle, great-circle distances are often used as approximations of geodesics for the purposes of air and sea navigation.

### great-circle bearing

    The horizontal direction or bearing followed by the arc of a great circle through a given pair of terrestrial points, expressed as the angular distance from a reference direction.

### great-circle distance

    The length of a line between two points which follows the arc of a great circle as defined by the intersection of the Earth's surface with an imaginary plane passing through the Earth's center. It is the shortest route between those two points on the Earth's surface.

### green belt

    A special land-use zone designated in some cities to prevent development of wild, largely undeveloped, or agricultural land surrounding or adjacent to urban areas, in order to conserve natural ecosystems, to allow the return and establishment of wildlife, and/or to create urban green space for aesthetic or recreational purposes. The term may also refer more specifically to the boundary between developed and undeveloped areas rather than to the undeveloped area itself.

### grid

    A pattern of lines on a chart or map, such as those representing latitude and longitude, which helps determine absolute location.

### grid magnetic angle

    The angular difference in direction between grid north and magnetic north, typically expressed in degrees east or west of grid north.

### grid north

    The direction northwards as indicated by the grid lines of a map projection, which may or may not be aligned with geodetic north and magnetic north.

### grivation

    See grid magnetic angle.

### groundwater

    The water present beneath the Earth's surface in soil pore spaces and in fractures and voids within geological strata. Contrast surface water.

### grove

    A small group of trees growing close together and generally surrounded by little or no undergrowth.

### growing season

    The part of the year during which local weather conditions (i.e. temperature and precipitation) permit the normal growth of plants in a given location. What defines a "growing season" is often informal and colloquial, and may vary widely by location and from year to year; in many places, the local growing season is defined as the period of time between the average date of the last frost (in temperate parts of the Northern Hemisphere, this typically occurs in the spring) to the average date of the first frost (in the autumn).

### groyne

    A rigid, man-made hydraulic structure extending from an ocean shore or river bank, constructed to interrupt water flow and limit the movement of sediment by longshore drift.

### gulch

    A deep, V-shaped valley formed by erosion, often containing a small stream or a dry streambed, especially one in arid regions.

### gulf

    A large arm or inlet of an ocean or sea that lies within a curved coastline, similar to a bay but usually larger and often with a narrower opening.

### gully

    A landform resembling a large ditch or a small ravine created by the action of swift running water eroding deeply and sharply into soil, typically on a hillside.

### gumbo

    Any very fine, clayey soil which rapidly turns to sticky mud when wet. The term is used primarily in the United States and Canada.

### guyot

    An isolated underwater seamount with a flat top that is at least 200 metres (660 ft) below the water's surface.

### gyre

    Any large system of circulating ocean currents, particularly those related to large-scale wind movements. Gyres are caused by the Coriolis effect and play a fundamental role in the global thermohaline circulation.

### gyroscope

    A device consisting of a spinning disc or rotor mounted in such a way as to preserve the orientation and angular velocity of its axis of rotation with respect to an inertial reference frame, irrespective of perturbations to the mounting itself, which makes it possible to measure and maintain an unbiased equilibrium in the attitude and/or course of a moving object such as an airborne or waterborne vehicle or camera. Modern digital gyroscopes and their associated readouts are widely used in navigation and geodesy as the basic sensor in direction-seeking, direction-keeping, and attitude stabilization systems.
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## H

### habitus

    An individual's sense of "home", or of their place in the world, comprising socially ingrained habits, beliefs, skills, and dispositions based on their geographical environment, cultural origin, inheritance, experiences, and the social networks they develop throughout their life, all of which may be subject to refashioning with passing time or increasing distance.

### hachure

    Any of a series of non-numerical lines used on a map to indicate the general orientation and steepness of topographical terrain. Such lines vary in length, thickness, and spacing, with steeper slopes indicated by shorter, heavier, and more closely spaced lines.

### haff

    A coastal lagoon of fresh or brackish water on the south coast of the Baltic Sea, fed by a stream which is blocked by a nehrung, through which it is linked to the sea by a channel.

### halo effect

    In the context of geography, the detrimental effect of a border or other boundary on locations close to it, making those locations unattractive to people intending to visit or settle there; e.g. a political boundary in disputed territory, where immigration across the boundary occurs frequently. There may also be beneficial effects on such locations.

### ham

    In southern England, a plot of meadow land, especially a tract of rich pasture near a river; or a small settlement, ranging in size from a single homestead to a town.

### hamada

    A desert landscape consisting of high, largely barren, rocky plateaus where most of the sand has been removed by deflation, and thus lacking most surficial materials other than boulders and exposed bedrock.

### hamlet

    A small human settlement, variably defined as one the size of a town, village, or parish or as a smaller subdivision of or satellite entity to a larger settlement.

### hanging valley

    A tributary valley that is higher in elevation than the main valley into which it drains, such that it appears to be "hanging" above the lower valley. Hanging valleys are commonly the result of differential glacial erosion, when adjacent areas beneath a glacier are subjected to different rates of erosion.

### harmonic tremor

    One of a series of continuous rhythmic earthquakes in the Earth's upper lithosphere that can be detected by seismographs. Harmonic tremors often precede or accompany volcanic eruptions.

### head of navigation

    The farthest point above the mouth of a river that can be navigated by watercraft, whether because of natural or man-made obstacles.

### heading

    The compass direction in which the bow or nose of a moving vessel or aircraft is pointed. This is not necessarily the same direction in which the vessel is actually traveling, known as its course; any difference between heading and course is due to the motion of the air or water through which the vessel is moving, or other aerodynamic effects such as skidding or slipping. See also bearing.

### headland

    A high coastal promontory that extends out into a body of water, often surrounded by steep cliffs. A very large headland is often called a cape.

### headwall

    A steep slope or sheer cliff face at the upper end of a valley (e.g. at the back of a cirque), or at the active face of a mine, pit, or quarry.

### headwaters

    1. Another name for the source of a river, stream, or other watercourse, i.e. the point or points furthest from the mouth of a particular stream, at which precipitation, meltwater, or groundwater first accumulates into a persistent, identifiable, and/or named body of water whose contents ultimately empty into the particular stream; or all of the uppermost streams of a watershed considered collectively (of which there may be thousands), typically including all streams identified as first-order through third-order in conventional stream order systems.
    2. The entire region, inclusive of land, surrounding these sources, often abutting the boundary of a drainage divide that separates different watersheds.

### hearth

    The source area of any innovation. The source area from which an idea, crop, artifact, or good is diffused to other areas.

### heartland

    1. The central or interior part of a region.
    2. A part of a region considered essential to the viability and survival of the whole.

### heath

    A shrubland habitat found mainly on free-draining, infertile, acidic soils and characterized by open, low-growing, woody vegetation.

### hectare (ha)

    A metric unit of area defined by a square with sides of 100 metres, equal to 10,000 $m^2$ or 2.471 acres. There are 100 hectares in 1 square kilometre $(km^2).$

### hedgerow

    A line of closely spaced shrubs or trees, planted and trained so as to form a barrier, to mark the boundary between two neighboring areas, or to serve as a windbreak for crops in adjacent fields.

### heliotrope

    A device used in geodetic surveying to reflect sunlight onto a distant point so as to aid long-distance observations.

### hemisphere

    One half of the Earth, usually conceived as resulting from the division of the globe into two equal parts of either north and south or east and west.

### heteroclinal fold

    A geological fold of which one side is sloped at an angle steeper than that of the other side.

### high plain

    A plain lying at a high elevation, generally above 600 metres (2,000 ft).

### high water mark

    A natural or man-made demarcation that indicates the maximum rise of a body of water over land. Though not necessarily an actual physical mark, river or sea waters rising to a high point often leave a lasting physical impression such as a noticeable discoloration or deposition of debris; such a mark is often the result of a flood or storm surge. High water marks may reflect an all-time high, an annual high, or the high point for some other division of time (e.g. a tidal cycle). A natural delineation created by debris deposited by a high tide is called a strandline. See also wash margin and mean high water.

### highland

    1. Any elevated region of land, often one that is mountainous or situated atop a plateau. The term is sometimes reserved for relatively low-elevation mountain ranges or foothills.
    2. Any area of land (mountainous or otherwise) that is higher in elevation relative to another area. In this sense, the term is often used as a conditional descriptor to distinguish related habitats or ecosystems, especially freshwater riparian areas, on the basis of elevation above sea level.

### highway

    Any major public or private road or other thoroughfare on land, especially one that is paved and capable of supporting high-capacity, rapid transit between populated places.

### hill

    Any landform that extends above the surrounding terrain. A hill is generally considered less steep than a mountain.

### hillock

    A small hill.

### hinterland

    1. An area that is tributary to a place and linked to that place through lines of exchange or interaction.
    2. The area, not necessarily settled itself, that is nonetheless influenced by a particular settlement or establishment, i.e. its sphere of influence.

### historical geography

    A branch of human geography that studies the ways in which geographic phenomena have changed over time, especially (though not necessarily limited to) geographic change as it relates to human activity; the geography of the past, whether real, perceived, or theoretical.

### hoe

    A projecting ridge or outcropping of land, its height ending abruptly or steeply. The term is used primarily in placenames in Great Britain.

### hogback

    A long, narrow ridge or series of hills with a narrow crest and steep, symmetrical slopes of nearly equal inclination on both flanks, especially one created by the differential erosion of an outcropping which exposes homoclinal sedimentary rock strata. Compare esker, drumlin, and cuesta.

### holding

    Land owned or occupied by legal right for the purpose of agriculture.

### homestead

    1. (dwelling) A house or home, especially an isolated farmhouse with its associated outbuildings on a large agricultural holding such as a ranch; or a small rural settlement of dispersed farms.
    2. (legal concept) In the United States, a plot of land given legal meaning by a series of federal laws granting applicants ownership of land in the public domain upon the condition that they live on it and improve it. Homesteaders were initially granted plots of 160 acres (0.65 $km^2),$ which was considered adequate to support a single family, but later as much as 640 acres (2.6 $km^2).$

### horizon

    The apparent line that separates the ground from the sky, dividing all visible directions into two categories: those that intersect the Earth's surface and those that do not. When not obscured by buildings, trees, or mountains, the true horizon can be useful in navigation and determining positional orientation. In perfect visibility, to an observer on Earth standing at an elevation of 3 metres (10 ft) from the horizontal, the horizon in any direction is approximately 6.5 kilometres (4 mi) distant; at 30 metres (100 ft), it is 21 kilometres (13 mi) away.

### horizontal equivalent

    The distance between two points on a land surface when projected on to a perfectly horizontal (i.e. flat) plane, e.g. on a map, as opposed to measuring the actual physical length along the real-world surface, which can be greatly increased by slopes and other topographic variations. The distance between the start and end points of any route, even if at the same elevation, will often appear to be much shorter on a map than the shortest route that could actually be walked between them, because of the influence of real-world changes in vertical displacement along the path followed by the route.

### horn

    A mountain formed by the back-to-back abutment of three or four adjacent cirques, leaving a distinctly pyramidal peak.

### horst

    A raised block of the Earth's crust, bounded by parallel escarpments or faults, that has been displaced upward or has remained stationary while adjacent blocks on either side, known as grabens, have been displaced downward. Horsts and grabens often occur side-by-side in a repeated series of vertical displacements.

### hotspot

    An area in the middle of a lithospheric plate where magma rises from the mantle and erupts at the Earth's surface. Volcanoes sometimes occur above a hotspot.

### hum

    A residual hill in limestone country, resembling a haystack, left standing when the surrounding land surface is eroded.

### human geography

    The branch of geography that studies humans and their communities, cultures, economies, and interactions with the environment by examining their relations with and across space and place. Along with physical geography, it is one of the two major sub-fields of geography.

### humanistic geography

    An approach in human geography which emphasizes the subjective as distinct from the objective in that it stresses the importance of perception, creativity, thinking, and beliefs as well as human experience and values in the formation of the attitudes of people toward their environment and in affecting their relationships with it.

### hummock

    A small knoll or mound, typically less than 15 metres (49 ft) in height and situated above an otherwise level ground surface.

### humus

    Partially decomposed organic soil material.

### hundred

    In England, Scandinavia, and many other parts of the world, an administrative subdivision of a larger region, often a county or shire, with its own judicial authority.

### hydrography

    The study of the surface waters of the Earth.

### hydrograph

    A graph showing the rate of flow (i.e. the discharge) of water past a specific point of measurement in a river or other channel over time, typically expressed in cubic metres or cubic feet per second $(m^3$ or $ft^3/s).$

### hydrosphere

    The totality of the water found on, under, and above the Earth's surface in liquid, solid, and gaseous forms, including all oceans, lakes, rivers, and streams, as well as all ice and glaciers and subsurface groundwater. Some definitions restrict the hydrosphere to liquid water only, instead placing solid forms in the cryosphere and gaseous forms in the atmosphere.

### hypsography

    The geographic representation on a map of features related to elevation, altitude, and other measures of height above a reference surface (and sometimes inclusive of depths below the reference surface as well).

### hypsometer

    Any instrument used to measure the height or elevation of an object above a reference surface, either by trigonometry or by measuring changes in atmospheric pressure or boiling point. Trigonometric principles are applied when viewing the measured object from a distance, e.g. when determining the heights of trees or buildings, or when surveying the elevations of distant landforms; whereas the principle that atmospheric pressure decreases predictably with elevation above sea level is applied in instruments that measure their own height (i.e. the elevation of the instrument's location).

### hypsometry

    The study or measurement of the elevation or depth of features of the Earth's surface relative to mean sea level. In a narrower sense, hypsometry may refer to land elevations only, and therefore is sometimes viewed as the terrestrial equivalent of bathymetry.
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## I

### ice age

    Any very long period of Earth's history during which surface and atmospheric temperatures are greatly reduced, resulting in the development or expansion of continental and polar ice sheets and widespread glaciation. The most recent such period was the Pleistocene Epoch, which ended approximately 12,000 years ago.

### ice cap

    A flattened, often dome-shaped mass of ice that covers less than 50,000 square kilometres (19,000 sq mi) of land area and is not constrained by topographical features such as mountains; larger masses of ice are termed ice sheets. Contrast polar ice cap.

### ice floe

    A large piece of floating drift ice, typically with a flat surface and at least 20 metres (66 ft) across at its widest point.

### ice sheet

    A mass of glacial ice that covers more than 50,000 square kilometres (19,000 sq mi) of land area; smaller masses of ice may be termed ice caps or ice shelves. The two polar ice sheets are the only ice sheets that currently exist on Earth.

### ice shelf

    A large floating platform of ice formed when a glacier or ice sheet in a coastal area flows onto the ocean surface. By contrast, sea ice is formed directly over the water and is typically much thinner.

### ice stream

    A region of relatively fast-moving ice within an ice sheet that flows like a stream under its own weight (making it essentially equivalent to a glacier) and empties into the ocean. Ice streams are responsible for the majority of the mass lost from both the Antarctic and Greenland ice sheets.

### iceberg

    A large chunk of fresh water ice which has broken away from a larger body of ice (such as a glacier or ice shelf) and is floating freely in open water.

### icefall

    A portion of a glacier where a steepening or narrowing of the underlying bed causes the ice to move more rapidly than elsewhere, resulting in a chaotic, highly fractured surface characterized by numerous crevasses and seracs.

### igneous rock

    Rock formed when molten (melted) materials harden.

### impact crater

    A type of crater formed by the hypervelocity collision of a solid astronomical body, such as a meteor, with the Earth's surface. Unlike volcanic craters, impact craters typically have raised rims higher in elevation and depressed floors lower in elevation than the surrounding terrain.

### impoundment

    1. Another name for a dam that impounds a body of water.
    2. The reservoir created by such a dam.

### improved land

    Any land area which has been intentionally altered from its natural condition by human activity, such as ploughing, clearing, cultivation, or some other form of management, and thereby made more valuable or productive for human purposes (not necessarily to the benefit of any other organism or the environment in general). Legal definitions vary with location, but in most countries the term refers primarily to certain types of agricultural land or to property which has been developed for residential or commercial use.

### inclinometer

    An instrument used to measure angles of slope, elevation, or depression with respect to the direction of the gravitational force, i.e. in the vertical plane, including both inclines and declines. The measure may be expressed in degrees, percentage points, or topos.

### index contour

    A contour line drawn with a heavier line weight to distinguish it from intermediate contours. Depending on the contour interval, index contours are usually indicated every fourth or fifth contour, along with their assigned numerical values, in order to facilitate ease of interpretation.

### inertia costs of location

    Costs borne by an activity because it remains located at its original site, even though the distributions of supply and demand have changed.

### influent

    (of a stream, river, or any natural water flow) Flowing into a larger watercourse or body of water.

### infrastructure

    The broad set of facilities and interrelated systems that serve a city, country, or any other inhabited area, encompassing the structures and services necessary for its industries, economies, and residential spaces to function, i.e. for the human population occupying these spaces to get what they want or need when they want or need it. Infrastructure may include public and private physical structures such as roads, railways, bridges, tunnels, water reservoirs, canals, sewers, and electrical and telecommunications networks, among other things. A well-developed infrastructure is essential to enable, sustain, and improve living and working conditions in any society or organization.

### ingression coast

    A generally flat coastline whose shape has been largely defined by the penetration of the sea into relatively low-lying areas of the land surface, often as a result of crustal movements or a rise in sea level, such that the boundary between land and water closely matches the topographic contours of the land prior to its being covered by seawater.

### inland

    Of, relating to, within, or towards the interior of a landmass, i.e. distant from the coast.

### inland sea

    A very large, isolated expanse of open water in the interior of a landmass, either completely surrounded by dry land or connected to the ocean by a river, strait, or other narrow waterway.

### inland waters

    Any surface watercourse or body of water surrounded entirely by land, including ponds, lakes, reservoirs, and rivers, or all such waters within a polity considered collectively. See also internal waters.

### inlet

    An indentation of a shoreline, usually long and narrow, which leads to an enclosed body of salt water, such as a sound, bay, lagoon, or marsh.

### inselberg

    An isolated rocky hill, knob, ridge, or small mountain that rises abruptly from a virtually level surrounding plain. Compare mogote.

### inset

    A subsection of a map that is reserved for depicting another map of the same place at a different scale, often a smaller scale to show relative location within a larger geographic area (e.g. a country's location on the globe) or a larger scale to show increased detail (e.g. of public transit routes in a downtown area), or with different features or overlays in order to provide additional information that would be difficult to interpret if presented in the main map area. Insets are usually outlined with an obvious boundary to prevent confusion, and may include their own set of cartographic elements such as a scale, graticule, and legend.

### inshore

    (relative to a position on a body of water) Near to or moving towards the shore; shorewards of a position as opposed to seawards of it. See also onshore and offshore.

### insular

    Of or relating to an island, or suggestive of the isolated condition of an island.

### integrated drainage

    A drainage pattern in which stream systems have developed to the point that all parts of the landscape drain into some part of a stream and to a common base level, the initial or original surfaces having essentially eroded away entirely, such that few or no closed drainage systems are present.

### integrated geography

    The branch of geography that describes and explains the spatial aspects of interactions between human individuals or societies and their natural environment.

### intercardinal directions

    The set of four intermediate directions used in cartography and navigation, each of which is located halfway between a pair of cardinal directions: northeast (NE), southeast (SE), southwest (SW), and northwest (NW). They are often included in the compass rose and are used to define further subdivisions such as the secondary-intercardinal directions.

### interfluve

    A narrow, elongated, and plateau-like or ridge-like landform between two valleys, or an area of higher ground between two rivers in the same drainage basin.

### intermediate directions

    See intercardinal directions.

### intermontane

    Situated between mountains or mountain ranges, e.g. the high plateaus lying between the eastern and western ranges of the Andes.

### International Date Line

    A line of longitude generally 180 degrees east and west of the Prime Meridian. The date is one day earlier to the east of the line.

### interpolation

    In geographic information science, the estimation of the values of spatially dependent variables at unsampled points based on known values of surrounding points, under the assumption that any unknown quantity can be calculated based on its distance to each surrounding quantity. Interpolation techniques such as spline and kriging are commonly raster operations, but can also be applied in vector environments using a triangulated irregular network to model a surface.

### interruption

    Any place where the contiguous geographic area represented in a map projection has been split, separating to distant parts of the projection certain features and locations which are in reality much closer to each other, in order to permit the representation of a three-dimensional space on a two-dimensional map. All world maps, for example, have at least one interruption, conventionally along the length of a single meridian, thus forming an east–west boundary despite that the approximately spherical shape of the Earth is continuous, with no such boundaries; features on either side of the interruption, though very close to each other on the actual Earth, are depicted on opposite edges of the map, appearing to be separated by thousands of miles. Some world map projections attempt to reduce distortion of scale by having more than one interruption, which divide the projected area into multiple gores, each with its own central meridian.

### intervening opportunity

    The existence of a closer, less expensive opportunity for obtaining a good or service, or for a migration destination. Such opportunities lessen the attractiveness of more distant places.

### Intracoastal Waterway (ICW)

    A system of navigable inland waterway channels, maintained through dredging and sheltered for the most part by a series of linear offshore islands, that follows the Atlantic and Gulf Coasts of the United States more than 4,800 kilometres (3,000 mi) from Boston, Massachusetts, around the southern tip of Florida, to Brownsville, Texas.

### inversac

    See estavelle.

### island

    Any piece of sub-continental land that is entirely surrounded by water; or more generally, any isolated habitat that is surrounded by a different habitat, including different types of land.

### island nation

    A country or polity whose territory consists primarily or entirely of one or more islands or parts of islands.

### islet

    A very small island.

### isometric

    Having equal measure.

### isopleth

    Any line on a map connecting places of equal value of some specified variable. The variable may be a physical or natural quantity, such as elevation above sea level (as with contour lines) or temperature (as with isotherms), or a quantity related to social or economic statistics, such as population, wealth, or transport costs.

### isostasy

    The state of gravitational equilibrium between the Earth's crust and its mantle, such that the crust "floats" at an elevation that depends on its thickness and density. This concept is invoked to explain how different topographic heights can exist at Earth's surface. Isostatic theory maintains that where equilibrium exists at the surface, equal mass must underlie equal surface area, and that the thickness of crustal features and the depth of the world's oceans tend to change over time in order to compensate for the uneven distribution of mass in the lithosphere. For example, the instability of continental margins where high mountains are found adjacent to deep oceanic trenches is explained by the subterranean movement of magma to effect a return to regional equilibrium, a process known as isostatic adjustment.

### isthmus

    A narrow piece of land connecting two larger land areas across an expanse of water by which they are otherwise separated.
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## J

### jetty

    Any man-made structure that projects from land out into a body of water, serving as a breakwater, a walkway, or a landing stage for watercraft, or, in pairs, as a means of constricting a channel.

### jhum cultivation

    Clear-cutting and/or setting fire to an area of land so it can be used for farm cultivation.

### junction

    A meeting or intersection of two or more routes of travel, as of roads, rivers, or lines on a map, or a place at which a single route diverges into two or more different routes.

### jungle

    An area covered with dense vegetation dominated by large trees, often tropical.

### jurisdiction

    1. The right and power to apply the law in a particular place or within a defined field of responsibility.
    2. The geographical area to which such authority applies.

## K

### kame

    An irregularly shaped hill or mound composed of sand, gravel, and glacial till which accumulates in a depression on a retreating glacier and is subsequently deposited on the land surface with further melting of the glacier. Kames are often associated with kettles.

### karre

    A furrow or channel varying in depth from a few millimetres to more than a metre, and separated from others by ridges, caused by solution on limestone surfaces.

### karst

    An area possessing surface topography resulting from the underground solution of subsurface limestone or dolomite.

### kettle

    A shallow, sediment-filled body of water formed by blocks of ice calving from a retreating glacier, or by draining floodwaters.

### key

    See cay.

### kill

    A river, stream, strait, or tidal inlet. The term is used primarily in areas of Dutch influence in the northeastern United States.

### knickpoint

    1. A point of abrupt inflection in the longitudinal profile of a river or its channel or valley, such as occurs at a waterfall.
    2. Any interruption or break in the character of a slope.

### knob

    A peak or projection from the top of a hill or mountain, or any rounded protrusion of land, especially a small but prominent or isolated hill with steep sides; a boulder or an area of resistant rock protruding from the side of a hill or mountain. The term is used primarily in the southern United States.

### knoll

    See hillock.

### kolk

    1. A violently rotating underwater vortex capable of plucking and scouring depressions in bedrock, which may leave behind distinct pits or lakes known as rock-cut basins or potholes.
    2. Another name for a bog pond.

### kopje

    See tor.

### krai

    In Russia and other Slavic countries, a generic term for a region, historically and politically reserved for border regions in particular, and variously translated as march, frontier, or territory. The term is cognate with the name of Ukraine.

### kriging

    In geostatistics, an interpolation technique in which, for a given spatially dependent variable, a predicted value for an unmeasured location is derived by weighting the surrounding measured values based on the distance between them and to the unmeasured location, as well as the overall spatial arrangement of the measured points. Widely used in GIS applications, kriging is based on regionalized variable theory, which assumes that the spatial variation in the data being modeled is homogeneous across the surface.

### kum

    A sandy desert of Central Asia, roughly equivalent to the Saharan erg.

### kyle

    In Scotland, a narrow channel or strait between two islands, or between an island and the mainland.
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## L

### lacustrine

    Of or pertaining to a lake; formed by or deposited in a lake.

### lacustrine plain

    A nearly level land area formed by the infilling of a lake with sediment and the complete drainage or evaporation of water from the lake, leaving the deposited sediments behind.

### lagoon

    A small area of water connected to the ocean but otherwise blockaded by one or more islands.

### lahar

    See mudflow.

### lake

    A body of water localized in a basin and surrounded entirely by land. Lakes are often defined as separate from any river or stream that serves to feed or drain them.

### land bridge

    Any piece of land connecting larger land areas that are otherwise separated by water, especially one over which living organisms, such as terrestrial animals and plants, are able to cross and thereby colonize previously inaccessible lands. Land bridges may be created by falling sea levels, tectonic activity, or post-glacial rebound. Compare isthmus.

### land cover

    The physical material present on the surface of the Earth, including categories such as vegetation (grasslands, shrubs, forests, etc.), bare ground, water, asphalt and artificial surfaces, and many others.

### land-tied island

    See tied island.

### landform

    A natural feature of the solid surface of the Earth. A combined set of landforms makes up the terrain of a given area, and their arrangement in a landscape is known as topography.

### landmark

    Any natural or artificial feature that is recognizable enough to be used for navigation; a feature that stands out enough from its environment to be visible across long distances.

### landmass

    Any large contiguous area of land typically surrounded by an ocean or sea. Compare continent.

### landscape

    1. A broad or distinct area of land consisting of a collection of landforms which define a general geomorphologic form or setting, e.g. a mountain range, valley, plain, coast, etc. Landforms within a landscape are spatially associated but may vary in formation processes and age.
    2. The visible features of an area of land, its landforms, and how they integrate with natural or man-made features. In the broadest sense, landscapes may include geophysical landforms such as hills and mountains; bodies of water such as rivers, lakes, and the sea; living elements of land cover such as vegetation; human elements such as buildings, structures, and various forms of land use; and transitory elements such as lighting and weather conditions. They reflect both physical origins and the cultural overlay of human presence in a living synthesis of people and place.

### lateral blast

    A sideways-directed explosion from the side or summit of a volcano.

### latitude

    A measure of distance north or south of the Equator. One degree of latitude equals approximately 110 kilometers (68 mi). Lines of latitude, also called circles of latitude or parallels, are the imaginary lines that cross the surface of the Earth in an east-west direction (parallel to the Equator) and measure how far north or south of the Equator a place is located.

### lava

    The term used for magma once it has erupted onto the Earth's surface.

### layer of no motion

    In oceanography, a hypothetical layer at some depth in the ocean within which the water is assumed to be at rest, implying that the isobaric surfaces within that layer are level and hence that such surfaces can be used as points of reference when calculating absolute-gradient currents.

### lea

    A pasture, meadow, or grassy field.

### leaching

    A process of soil nutrient removal through the erosive movement and chemical action of water.

### lee

    The side or slope of a physical feature (such as a hill or mountain) which faces downwind, i.e. away from the direction in which the wind is blowing, or which faces away from an advancing glacier or ice sheet. The lee side is often sheltered by the topography from exposure to the wind and any moisture it brings.

### leeward

    Toward the lee side; sheltered from the wind; the direction downwind from a point of reference. Contrast windward.

### legend

    A key for understanding the meanings of the symbols or pictures on a map.

### LEDC

    An acronym for Less Economically Developed Country.

### levee

    An elongated naturally occurring ridge or an artificially constructed wall or barrier which regulates water levels in areas prone to flooding. It is usually earthen and often parallel to the course of a river or a coastline.

### lithosphere

    The Earth's hard, outermost shell. It comprises the crust and the upper part of the mantle. It is divided into a mosaic of 16 major slabs or plates, which are known as lithospheric plates or tectonic plates.

### lithospheric plates

    A series of rigid slabs (16 major ones at present) that make up the Earth's outer shell. These plates float on top of a softer, more plastic layer in the Earth's mantle.

### loam

    A type of easily worked, highly fertile soil composed of clay, silt, and sand in an approximate ratio of 20:40:40. Loams generally heat rapidly, are well-aerated, and drain neither too quickly nor too slowly.

### location

    A particular point or place in physical space. Compare absolute location.

### location theory

    A group of theories which seek to explain the siting of economic activities in particular locations.

### loess

    A soil made up of small particles that were transported by the wind to their present location.

### longitude

    A measure of distance east or west of the Prime Meridian, a line drawn between the North and South Poles and passing through the Royal Observatory at Greenwich, England. Lines of longitude, also called meridians, are the imaginary lines that cross the surface of the Earth in a north-south direction (parallel to the Prime Meridian) and measure how far east or west of the Prime Meridian a place is located.

### lowland

    Any area of land that is lower in elevation relative to another area. The term is often used as a conditional descriptor to distinguish related habitats or ecosystems, especially freshwater riparian areas, on the basis of elevation above sea level. Lowland areas are usually relatively flat and characterized by slow-flowing waterways and alluvial plains. Contrast highland and upland.
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## M

### maar

    A broad, shallow, flat-bottomed volcanic crater created by an eruption involving groundwater coming into contact with magma. Maars commonly have low rims and subtle relief and characteristically fill with water to form crater lakes.

### machair

    A fertile, low-lying, grassy plain on the northwest coasts of Ireland and Scotland.

### magma

    Molten rock containing liquids, crystals, and dissolved gases that forms within the upper part of the Earth's mantle and crust. When erupted onto the Earth's surface, it is called lava.

### magmatic water

    See juvenile water.

### magnetic anomaly

    A local deviation from the predicted value of the Earth's magnetic field, due either to the presence of rocks formed in past geological eras which have preserved internal magnetizations that differ from modern magnetic alignments, or to local abundances or deficiencies of ferromagnetic minerals.

### magnetic declination

    The angle on the horizontal plane between magnetic north and true north. Because compass needles always point to magnetic north, and because the Magnetic North Pole and the Geographic North Pole are not in precisely the same location, the north direction indicated by a compass may be slightly different from the direction of geographic north, depending on the user's location on the Earth. The user can compensate for this discrepancy by adding the known declination angle for their location to the magnetic bearing reported by their compass, yielding the true bearing with respect to true north.

### magnetic dip

    The angle made with the horizontal by the Earth's magnetic field lines. Locations in the Northern Hemisphere usually have positive values of inclination, indicating that the magnetic field is angled downward, into the Earth; the angle increases as one approaches the North Magnetic Pole, where the field lines point vertically downward, perpendicular to the horizontal. Locations in the Southern Hemisphere usually have negative inclination, indicating that the field lines are angled upward, away from the Earth, with the maximum angle located at the South Magnetic Pole. Dip angle is in principle the angle made by the needle of a vertically held compass, though in practice ordinary compass needles may be deliberately weighted against dip, or may be unable to move freely in the correct plane. Magnetic dip can be measured more reliably with a dip circle.

### magnetic north

    The direction a compass points, towards the Magnetic North Pole. Magnetic north differs from true north and grid north.

### magnetic pole

    Either of the two poles of the Earth's true magnetic field – the Magnetic North Pole or the Magnetic South Pole.

### magnetic variation

    See magnetic declination.

### main stem

    The primary downstream channel of a river, as contrasted with its tributaries. Virtually all of the water in a river's drainage basin eventually flows through the main stem.

### mainfall

    See grade.

### mainland

    A term used to denote a contiguous landmass or political territory relative to its politically associated but geographically remote outlying territories. It is variously used to refer to the continental (i.e. non-insular) part of a polity relative to its exclaves or oceanic islands; or to the largest or most politically, economically, and/or demographically significant island within an island nation. For example, continental Europe is often considered "the mainland" relative to the British Isles, while the island of Great Britain is considered "the mainland" relative to Northern Ireland and the many smaller islands that constitute the United Kingdom.

### makhtesh

    A deep, closed valley (usually drained by a single wadi) surrounded by steep walls of resistant rock and superficially resembling a crater. The term is used primarily in the deserts of Israel and Egypt.

### mammilated

    Smooth and rounded in appearance, used of various landforms of different sizes from individual rocks to entire landscapes.

### mantle

    The layer of the Earth's interior between the crust and the core, consisting of ultrabasic rock which is predominantly solid under the immense pressure of overlying rock but behaves as a viscous fluid over geological time scales or if this pressure is relieved (as with magma penetrating the crust). The mantle is about 2,900 kilometers (1,800 mi) thick, making up 84% of the Earth's volume and 67% of its mass. The uppermost sub-layer is known as the asthenosphere; the lithosphere is composed of the topmost 65–70 kilometres (40–43 mi) of the mantle and the crust.

### map

    A picture of a place drawn at an established scale on a two-dimensional plane surface, often depicting natural and manmade features on or under the surface of the Earth or other planetary body, typically with the features positioned as accurately as possible relative to a coordinate reference system; more generally, any graphical representation of locative information about the relative positions of particular features within a space or place.

### map index

    A graphical key identifying the relationships between the individual maps of a map series, their coverage areas, and/or their production status or availability. Index maps enable users to find a map or set of maps covering a particular region of interest by overlaying a grid or a set of rectangles on a map of a larger geographical area. Each grid unit or rectangle is labeled with a name or number corresponding to a specific map sheet which depicts the indicated area in greater detail.

### map projection

    A systematic transformation of the latitudes and longitudes of locations from the surface of a three-dimensional shape, such as a sphere or an ellipsoid, into locations on a two-dimensional plane. Maps of locations on the Earth require map projections to represent features in a convenient format that is easy to view and interpret, though all map projections necessarily distort the true properties of the Earth's surface to some degree.

### map series

    A group of topographic or thematic map sheets usually having the same scale and cartographic specifications and collectively identified by the publisher or producing agency as belonging to the same group.

### map sheet

    An individual map or chart printed on a single page or sheet of paper, either complete in itself or part of a map series.

### mapping

    The process of designing, drawing, or creating a map. The term is used in particular to refer to the application of cartographic techniques in order to make planimetric or topographic maps, but may also be used for any map, and in the broadest sense may refer to the gathering of geographical data of any kind.

### march

    A boundary, frontier, or borderland, as opposed to an interior heartland. In medieval Europe, a march was the land surrounding a border between realms, or a neutral buffer zone under the joint control of two or more realms with conflicting laws or territorial claims.

### margin

    1. The line or edge along which the surface of a body of water meets the land.
    2. In property law, the boundary of a piece of land which is bounded by a stream or watercourse, often with the center of the stream or the thalweg defining the legal boundary.
    3. The mostly blank, unused space lying beyond the neatline of a map and completely surrounding the map area. See also surround.

### marginal land

    Land that is of low agricultural value because any crops produced from it would be worth the same or less than the costs paid to produce them, either because the rights or improvements required to cultivate it are very expensive, or the market prices for the crops are very low, or for any other reason. A change in economic conditions may allow formerly marginal lands to become profitable again.

### marginal sea

    1. A sea or other large area of the ocean that is partially enclosed by land and/or submarine ridges yet still adjacent to, widely open to, and connected to the larger ocean at the surface; e.g. the Yellow Sea and Hudson Bay.
    2. Also territorial sea, marine belt, and maritime belt.Those waters along a nation's coast within which the nation has exclusive jurisdiction except for the right of innocent passage of foreign vessels. See also territorial waters.

### marine

    1. Of, relating to, found in, or produced by the sea or ocean.
    2. Of or relating to shipping or navigation, particularly by watercraft.

### maritime climate

    A climate strongly influenced by an oceanic environment, typically found on islands and the windward shores of continents. It is characterized by small daily and yearly temperature variation and high relative humidity.

### market orientation

    The tendency of a firm or industry to be located close to wherever demand for the commodities it produces is strongest.

### marsh

    A type of wetland dominated by herbaceous rather than woody plant species and often found at the edges of lakes and streams, where it forms a transition between aquatic and terrestrial ecosystems.

### massif

    1. Any section of the Earth's crust which is demarcated by faults or flexures and tends to retain its internal structure while being displaced as a whole.
    2. A single large mountain mass or compact group of connected mountains forming an independent portion of a mountain range.

### mayen

    In Switzerland and the Central Alps, a large shelf or ledge, intermediate between high alpine meadows and valley floors, where cattle are allowed to rest briefly during their annual movements between summer and winter pasture.

### mean sea level (MSL)

    The average sea level of one or more of the Earth's coastal bodies of water, such as oceans and seas, or at a particular location, from which heights such as elevation and altitude are measured.

### meander

    One of a series of regular sinuous curves, bends, loops, turns, or windings in the main channel of a river, stream, or other watercourse. Meanders are produced by the repetitive upstream erosion and downstream deposition of sediments along the banks of a watercourse as the water flows back and forth across the axis of a valley or floodplain.

### meander cutoff

    The process by which the strip of land separating the two closest parts of a meandering river or stream channel is breached by the river's flow, forming a new, shorter channel that effectively "shortcuts" the loop of the meander and causes it to be gradually abandoned until it is completely isolated from the main flow. The river's course suddenly becomes much straighter, and the abandoned meander often forms a slackwater or an oxbow lake, or becomes loaded with sediment and dries up entirely, leaving visible traces of the former channel.

### meander neck

    The narrow strip of land separating the river on each side of a well-developed meander. If this strip is completely eroded away, a cutoff occurs. See also neck.

### meander scar

    A typically crescent-shaped incision in a bluff or valley wall formed by the remnants of a dry, abandoned meander.

### MEDC

    An acronym for More Economically Developed Country.

### medial moraine

    The morainic debris lying centrally in a line across the surface of a glacier, formed when the lateral moraines of two confluent glaciers meet.

### medical geography

    A branch of human geography that studies the geographical aspects of health and the provision of healthcare, examining the spatial distribution of human diseases, mortality, morbidity, and the environmental factors conducive to human health and illness.

### Mediterranean climate

    Any climate characterized by mild, rainy winters and hot, dry summers, as experienced in the Mediterranean Basin.

### megacity

    A very large city, typically with a population of at least 10 million people. Precise definitions vary, but criteria are usually based on total population and/or population density.

### megalopolis

    A chain of roughly adjacent metropolitan areas which have merged into a very large and heavily populated urban complex. See conurbation and metropolitan coalescence.

### meilograph

    See opisometer.

### meltwater

    Water (usually freshwater) derived from the melting of snow or ice, including seasonal snowfall, glacial ice, icebergs, and ice shelves over the ocean.

### Mercator projection

    A conformal cylindrical map projection in which the equator is represented by a straight line true to scale and meridians are represented by parallel straight lines perpendicular to the equator and uniformly spaced according to the distances between them at the equator. Lines of latitude are also represented by a system of straight lines which are perpendicular to all of the meridians and therefore parallel to the equator, though their spacing is not uniform but rather increases with increasing distance from the equator in order to conform with the expanding scale resulting from the parallel representations of the meridians. The standard Mercator projection has long been popular in navigation because it represents north as up and south as down everywhere in the world while preserving local directions and shapes, though it also greatly inflates the size of objects near the geographic poles.

### mereing

    A type of surveying in which boundaries are established with respect to ground features present at the time of the survey, which may include natural features and may or may not remain unchanged over time, e.g. a metes and bounds survey.

### meridian

    A line of longitude, i.e. any imaginary line connecting points of equal longitude and running perpendicular to all lines of latitude, intersecting them at right angles. Unlike lines of latitude, meridians are all the same length, but are not parallel to each other, instead converging at the geographic poles. Each meridian is half of a great circle drawn on the Earth's surface; the other half, connecting all of the meridian's antipodes, is termed an antimeridian. Meridians are numbered according to their longitudinal measure in angular degrees (further subdivided into minutes and seconds) up to 180 degrees east or west of an arbitrarily designated zero or prime meridian, by convention the International Reference Meridian.

### meridional

    Of, relating to, or characteristic of the south, especially of the inhabitants of a southern region or territory, in particular southern Europe. Contrast septentrional.

### mesa

    An isolated, relatively flat-topped natural elevation, usually more extensive than a butte and less extensive than a plateau.

### metamorphic rock

    Rock that has been physically altered by heat and/or pressure.

### metes and bounds

    A system of land survey that defines land parcels according to visible natural landscape features and distance. The resultant field pattern is usually very irregular in shape.

### metropole

    The homeland or central territory from which a colonial empire governs, as opposed to its colonies or overseas territories.

### metropolis

    A large city or conurbation which is considered a significant economic, political, or cultural center for a country or geographic region and/or an important hub for regional or international connections and communications.

### metropolitan area

    A region consisting of one or more densely populated urban cores (often a metropolis) and its less populous surrounding territories, including satellite cities, towns, and intervening rural areas, all of which are socioeconomically tied to the core as typically measured by commuting patterns. A metropolitan area usually comprises multiple neighborhoods, jurisdictions, and municipalities, with its inhabitants sharing industry, housing, and many other forms of infrastructure.

### metropolitan coalescence

    The merging of the urbanized parts of separate metropolitan areas; a megalopolis is a result of this process.

### mire

    See bog.

### mogote

    An isolated, rounded, steep-sided hill composed of either limestone, marble, or dolomite and surrounded by nearly flat alluvial plains, especially as found in tropical regions.

### mole

    A long, massive, man-made stone or earthen structure used as a pier or breakwater, or as a causeway between places separated by water, but designed to prevent the free movement of water underneath it (unlike a true pier).

### monadnock

    See inselberg.

### montane

    Of or pertaining to a mountain or mountains; mountainous; occurring at high elevation. The term is used in particular to describe biomes or ecological communities occupying cool, humid zones at or near timberline. See also alpine.

### monticule

    A secondary cone on the side of a larger volcano, or any small mountain or large hill.

### moor

    An upland habitat and ecoregion characterized by low-growing vegetation on acidic soils and generally referring to uncultivated hills but also including low-lying wetlands.

### moraine

    The rocks and soil carried and deposited by a glacier. A terminal moraine, either a ridge or low hill running perpendicular to the direction of ice movement, is often visible near the end of a retreating glacier, indicating the glacier's maximum advance.

### moulin

    A vertical, cylindrical shaft, up to 25–30 metres (82–98 ft) deep, by which surface meltwater flows into a glacier, usually formed at lines of structural weakness in the ice.

### mound

    Any heaped pile of earth, gravel, sand, rocks, or debris, typically with a rounded top and of topographically higher elevation than its immediate surroundings.

### mountain

    A large landform that rises prominently above the surrounding land in a limited area, usually in the form of a rocky peak with great vertical relief; a mountain is generally considered steeper than a hill. Mountains are formed by volcanic or tectonic forces and erode slowly through the actions of rivers, glaciers, and weathering. Most exist within extensive mountain ranges.

### mountain pass

    A navigable route through a mountain range or over a ridge, often crossing a saddle.

### mountain range

    A series of neighboring mountains or hills, often closely arranged in a line and connected by high ground. Individual mountains within the same mountain range are usually the result of the same orogeny, and often (though not always) share a common form, alignment, and geology.

### mouth

    1. The place where a river or stream flows into another body of water, such as a lake or another river but especially a sea or ocean. Deltas and estuaries occur near the mouths of rivers.
    2. The lower or downstream end or the most accessible entrance of a valley, canyon, ravine, or cave.

### mudflat

    A type of coastal wetland consisting of exposed layers of bay mud formed by the deposition of silts, clays, and marine animal detritus by tides or rivers. Mudflats usually form within the intertidal zone of relatively sheltered areas such as bays and lagoons.

### mudflow

    A flowing mixture of water and debris (intermediate between a volcanic avalanche and a water flood) that forms on the slopes of a volcano.

### multilingual

    The ability to use more than one language when speaking or writing. This term often refers to the presence of more than two populations of significant size within a single political unit, each group speaking a different language as their primary language.

### municipal corporation

    The legal term for a government body at the local level, including but not necessarily limited to cities, counties, towns, townships, villages, and boroughs.

### municipality

    A type of general-purpose urban administrative subdivision having corporate status and powers of self-government or jurisdiction as granted by national and/or state laws to which it is subordinate. Municipalities are often included within but usually distinguished from larger administrative divisions such as counties, though the nature of their territorial boundaries and political jurisdictions can vary considerably in different parts of the world.

### muskeg

    Another name for a bog, used primarily in Alaska and western Canada.
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## N

### narrows

    A land or water passage that is confined or restricted by its narrow breadth, often a strait or a water gap.

### nation

    A stable community of people formed on the basis of a common geographic territory, language, economy, ethnicity, or psychological make-up as manifested in a common culture.

### national mapping agency

    A governmental agency which manages, produces, and publishes topographic maps, geographic data, and sometimes cadastral information that is specific to an individual nation or political territory, such as the United Kingdom's Ordnance Survey.

### national park

    A type of protected area created and managed as a public park by a national governmental authority for conservation purposes. Though individual governments designate national parks differently, they usually share the common goal of preserving natural or semi-natural landscapes (often wilderness) for posterity and as symbols of national pride.

### natural landscape

    The original landscape that exists before it is acted upon by humans. Contrast cultural landscape.

### navigation

    1. The determination of position and direction, generally by comparing the navigator's position to known locations or patterns.
    2. The process of monitoring and controlling the movement of a vehicle or craft from one place to another.

### neap tide

    A tide of decreased tidal range occurring semi-monthly as a result of the Moon being in quadrature with respect to the Earth and the Sun (i.e. in the first quarter or last quarter phases, when roughly half of the lunar disk is visible), or the time period recurring every 14 days during which such tides occur. The average height of the high waters of the neap tides occurring at a particular location is called neap high water or high water neaps, and that of the corresponding low waters is called neap low water or low water neaps. Compare spring tide.

### nearshore

    The part of a beach between the shoreline and the line at which the waves break.

### neatline

    A line separating the main body of a map from the map's margin. On a standard quadrangle map, the neatlines are the meridians and parallels delimiting the quadrangle.

### neck

    1. A narrow stretch of land with water on each side, e.g. an isthmus or promontory.
    2. A narrow stretch of woodland or of ice.
    3. A high level pass, especially the narrowest part.

### nehrung

    A long sandspit separating a haff or lagoon from the sea, especially one along the south coast of the Baltic Sea.

### neighborhood

    A geographically localized community within a larger city, town, suburb, or rural area, particularly one which supports considerable face-to-face interactions between residents.

### ness

    In Scotland and parts of England, a headland or cape, or another name for a cuspate foreland; or a spur of a mountain ridge.

### nodal region

    A region characterized by a set of places connected to another place by lines of communication or movement.

### North Geographic Pole

    The point in the Northern Hemisphere where the Earth's axis of rotation meets its surface. It is the northernmost point on Earth, directly opposite the South Geographic Pole, and defines the direction of true north at a latitude of 90 degrees North; its longitude can be assigned any degree value. Unlike the South Pole, the North Pole is not located on a continental landmass but in the middle of the Arctic Ocean. See also North Magnetic Pole.

### North Geomagnetic Pole

    The point in the Northern Hemisphere where the axis of a theoretical simplified dipole passing through the center of the Earth would intersect the Earth's surface. It is antipodal to the South Geomagnetic Pole. Because of the fluid nature of the Earth's molten core, the true axis of the Earth's magnetic field is not a perfect dipole, and so the Geomagnetic Poles and the actual Magnetic Poles lie some distance apart.

### North Magnetic Pole

    The point in the Northern Hemisphere at which the Earth's magnetic field points vertically downward. It is close to but distinct from the Geographic North Pole and the Geomagnetic North Pole, and its precise location varies considerably over time due to frequent magnetic changes in the Earth's core. Its counterpart in the Southern Hemisphere is the South Magnetic Pole, though the two poles are not directly opposite each other.

### Northern Hemisphere

    The half sphere of the Earth that is north of the Equator. It is opposite the Southern Hemisphere.

### nubbin

    A small, gentle hill consisting of a bedrock core dotted with rounded residual boulders. Nubbins form in a similar way to castle koppies and bornhardts.

### nunatak

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## O

### oasis

    A combination of a human settlement and an area of cultivated vegetation in an otherwise desolate desert or semi-desert environment, made fertile when sources of fresh water, such as underground aquifers, irrigate the surface naturally or via man-made wells.

### oblate spheroid

    The approximate geometric shape of the Earth: a three-dimensional ellipsoid that is nearly but not exactly a true sphere, being instead slightly flattened at the poles and slightly elongated at the equator.

### obsequent

    (of a stream, river, or any natural water flow) Flowing in the direction opposite to that of the dip of the underlying rock strata. Contrast consequent and subsequent.

### ocean

    The vast, contiguous body of salt water covering more than 70% of the Earth's surface area and surrounding the continental landmasses; or any portion of this larger body of water that is divided and distinguished from the other portions, each of which is called an ocean, by the presence of the landmasses. The International Hydrographic Organization recognizes five principal oceanic divisions on Earth: from largest to smallest, they are the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean, and Arctic Ocean.

### ocean floor

    See seabed.

### ocean trench

    A long, narrow, very deep depression in the ocean floor where, at the junction of two tectonic plates, one plate is subducted steeply beneath the other, often penetrating the mantle.

### oceanography

    The scientific study of the Earth's oceans and all processes and phenomena relating to them, including their formation and evolution over time; their physical and chemical properties and how these vary within the ocean and across its boundaries; their interactions with landmasses along coasts; the bathymetry and geology of the sea floor; currents, waves, and geophysical fluid dynamics; marine life and ecosystems; and how humans affect and are affected by oceans. The interdisciplinary field draws from and involves a diverse range of other sciences, including physics, biology, geology, hydrology, meteorology, and climatology, among others.

### oecumene

    See ecumene.

### offshore

    1. Moving away from the shore and toward the sea.
    2. Located at a point or in an area that is relatively close to but still seaward of the shore (as with an offshore island). Contrast onshore.
    3. Seaward of the foreshore and the backshore.

### ogive

    One of a series of regularly spaced bands of alternating height and color visible on the surface of some glaciers, resulting from seasonal patterns of alimentation and ablation. Because ice flows faster near the center of the glacier, where there is less friction with the surrounding glacial bed, ogives are usually shaped into conspicuous arcs that point towards the terminus of the glacier.

### ojo

    In the southwestern United States, a small pond, lake, or spring, especially a hot spring.

### open ocean

    The part of the ocean that is beyond or outside of coastal areas, i.e. distant from land and not enclosed or partially enclosed by it. In oceanography, the term is synonymous with pelagic zone and is often defined as all oceanic waters seaward of any continental shelf; politically and economically, "open ocean" usually refers to all areas of a sea or ocean that are not within territorial waters (hence, any area that is within international waters) or, much more restrictively, not within any sovereign state's exclusive economic zone. See also high seas.

### open range

    A cattle- or sheep-ranching area characterized by a general absence of fences and in which livestock are by law allowed to roam freely.

### opisometer

    An instrument used to measure the lengths of arbitrary curved lines, especially the distances of rivers and roads on a map.

### ordinal directions

    See intercardinal directions.

### ordnance datum (OD)

    Any vertical datum used by the British Ordnance Survey as the basis for reporting elevations on maps. In modern Great Britain, the standard ordnance datum is the ODN, defined as the mean sea level calculated from hourly observations of the tidal gauge at Newlyn, Cornwall, between 1915 and 1921. All heights shown on British maps are measured from this benchmark.

### orientation

    The position of or the act of positioning a person or object with respect to the directional points of a compass, especially the placement of a map or surveying instrument in the field so that a north–south line on the map or instrument lies parallel to a north–south line on the ground. Determining one's orientation at a given time is the chief aim of orienteering, and is generally of critical importance in navigation.

### orographic rainfall

    Precipitation that results when moist air is lifted over a topographic barrier, such as a mountain range.

### orography

    A branch of physical geography and geomorphology concerned with the scientific study and description of the topographic relief of the Earth, particularly of mountains and hills, and more broadly of any elevated terrain.

### orthodrome

    See great circle.

### orthodromic distance

    See great-circle distance.

### orthophotograph

    An aerial photograph or satellite image that has been geometrically corrected or orthorectified such that the scale is uniform across all parts of the image, allowing the image to align with a particular map projection. In an uncorrected aerial photo, distances on the ground may be distorted by topographic relief, camera tilt, or the curvature of the Earth; techniques of digital image processing can compensate for these distortions, often by combining multiple images captured from slightly different perspectives into a single composite image. Orthophotos can be used to measure true distances because they accurately depict the relative sizes and positions of features on the Earth's surface.

### outback

    In Australia, the vast, remote, sparsely populated backcountry. See also bush.

### outcrop

    Any visible exposure of bedrock or ancient superficial deposits on the surface of the Earth; or more generally, any bare, rocky surface that is topographically distinct from the surrounding terrain. Outcrops occur frequently in places where the rate of erosion exceeds the rate of weathering, such as on steep hillsides and mountains, river banks, and coastlines.

### outwash

    Rocky and sandy surface material deposited by melted water that flows from a glacier.

### outwash plain

    A smooth, flat plain of sandy or gravelly alluvial sediment formed by outwash deposited in front of the toe of a melting glacier, with larger material deposited closer to the terminal moraine.

### overbank

    1. Alluvial sediment, usually consisting of fine sand, silt, and clay, that has been deposited on the floodplain of a river or stream by flood waters that have broken through or overtopped the river's banks.
    2. The stage when a river or stream overflows the banks of its normal channel and spreads on to a floodplain, depositing such sediment.

### overburden

    Uneconomic material covering a mineral seam or bed that must be removed before the mineral can be extracted in strip mining.

### oxbow

    1. A wide U-shaped meander in a river or stream.
    2. The lake formed when a meander is cut off from the main stem of the river, creating a separate body of water.
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## P

### Pacific-type coastline

    See concordant coastline.

### padang

    An uncultivated, treeless grassland in Southeast Asia, sometimes swamp-like, supporting a scrubby heath-type vegetation common on leached sandy soils.

### palisade

    1. A wall of wooden stakes used as a defensive barrier.
    2. A line of bold cliffs, especially one showing basaltic columns.

### palsa

    An elliptical dome-like permafrost mound containing alternating layers of ice lenses and peat or mineral soil, commonly 3–10 metres (10–33 ft) high and 2–25 metres (7–82 ft) long, and occurring frequently in bogs in the Arctic and subarctic zones of discontinuous permafrost.

### paludal

    Of or pertaining to a swamp or marsh, or to sediments that accumulate in a marshy environment.

### pampa

    In parts of South America, a vast, fertile, grassy plain; or the temperate lowland region encompassing these plains.

### pan

    Any shallow, generally rounded basin or hollow, which may seasonally capture and hold water from rainfall or snowmelt, especially one occurring in an arid or semi-arid region; more specifically, the flat central part of such a depression, which may be temporarily or seasonally flooded.

### panhandle

    See salient.

### panhole

    A rounded or circular depression eroded into flat or gently sloping cohesive rock, typically shallow and ranging in diameter from a few centimeters to several meters, that is capable of collecting and holding rainwater and snowmelt. The term is sometimes used interchangeably with pothole, though the latter may also refer to distinct geological features.

### pantanal

    In southern Brazil, a wetland region consisting of a usually dry savanna that is seasonally flooded by a river.

### pantograph

    An instrument that enables the mechanical copying of a map or technical drawing on a selectable scale, such that the movement of one pen, in tracing an image, produces identical movements in a second pen, resulting in a duplicate image that is the same size, enlarged, or miniaturized with respect to the original. Pantographs typically consist of hinged rods arranged in the shape of a parallelogram which rotate about a fixed point.

### parallel

    1. (geometry) Extending in the same direction, equidistant at all points, and never converging or diverging; having the same orientation, nature, tendency, or course; corresponding or similar.
    2. (geography) Another name for a circle of latitude.

### parish

    A type of subnational division of a country or federal state used for religious, administrative, or other purposes.

### pass

    See mountain pass.

### passive glacier

    A glacier with low rates of both alimentation and ablation because it receives only light snowfall and undergoes little melting throughout the year. Such glaciers move very slowly and transport relatively small amounts of ice and debris. Contrast active glacier.

### pasture

    Any land used for grazing by livestock, often a natural grassland supporting native grasses and forbs with little or no active management by humans, as opposed to a meadow, where the vegetation is mown for hay or silage.

### peak

    1. A pointed or protruding top or vertical projection on a landform, e.g. a mountain, especially implying the highest point or elevational maximum, i.e. the summit.
    2. A mountain as a whole, in particular a high, isolated, or prominent one.

### pediment

    An eroded, often bare rock platform, cut into the local bedrock, usually slightly concave and triangular in shape and extending over a considerable area at the foot of an abrupt mountain slope or face, the lower edge sloping gently away. Pediments form basal slopes of transport for weathered material derived from the steeper slope above, and are characteristic of arid and semi-arid lands.

### pedology

    The scientific study of the morphology, composition, and spatial distribution of soils, with an emphasis on classifying soils and understanding their formation and evolution.

### peninsula

    A piece of land surrounded by water along the majority of its border while still being connected to a mainland from which it projects.

### perennial stream

    A stream that normally flows continuously throughout the entire year, without drying up, as opposed to a transient or intermittent stream.

### periglacial

    1. Of or relating to an area located adjacent to or on the margin of an ice sheet or glacier, either presently or in the past; or to associated phenomena.
    2. Any place where seasonal cycles of freezing and thawing modify the landscape in a significant manner.

### periplus

    A historical manuscript listing the ports, safe anchorages, and coastal landmarks that a maritime vessel could expect to encounter along a shore or coastline, arranged in order according to a particular direction of travel and including the intervening distances between them. See also itinerarium.

### permafrost

    A permanently frozen layer of soil; permanently frozen ground at high latitude and high elevation.

### photic zone

    The uppermost layer of a body of water (e.g. a lake or ocean), defined by the maximum depth to which sunlight can penetrate the water column. The photic zone usually supports large populations of photosynthetic organisms and the majority of the aquatic life inhabiting the body as a whole.

### photogrammetry

    1. The science and technology of obtaining reliable information about physical objects and environments through the process of recording, measuring, and interpreting photographic images (usually aerial or orbital ones) and patterns of electromagnetic radiant imagery and other phenomena.
    2. The science of extracting three-dimensional measurements from two-dimensional data, such as images.

### phreatic water

    See groundwater.

### phreatic zone

    The part of an aquifer that is below the water table, where nearly all pores and fractures are fully saturated with water. Contrast vadose zone.

### physical geography

    The branch of geography that studies processes and patterns in the natural environment, such as the atmosphere, hydrosphere, geosphere, and biosphere, as opposed to the cultural or built environment. Along with human geography, it is one of the two major sub-fields of geography.

### physiographic region

    A portion of the Earth's surface with a common topography and morphology.

### physiography

    Another name for physical geography.

### piedmont

    Any geographic region lying or formed at the base of mountains. The term is used primarily in the southeastern United States to refer to a broad region extending from the Blue Ridge Mountains to the Atlantic coastal plain.

### pingo

    A periglacial landform consisting of a relatively large conical mound of soil-covered ice, commonly 30–50 metres (100–160 ft) high and up to 1,000 metres (0.6 mi) in diameter, and that grows and persists in part as a result of hydrostatic pressure within and below the permafrost of Arctic and subarctic regions.

### pit crater

    A type of crater formed by the sinking or collapse of the surface lying above a void or empty chamber. Pit craters are similar to calderas and are often associated with volcanic activity, but lack the ejecta deposits and lava flows of volcanic craters.

### place utility

    The measure of approval or satisfaction accorded by an individual to a location in his or her action space; the value or usefulness of a particular place as perceived by a particular person. Dissatisfaction with place utility may result in migration.

### placename

    See toponym.

### placer

    1. (mineral deposit) An accumulation of valuable minerals, particularly gold, formed by gravity separation from a source rock during natural sedimentary processes. The minerals, weathered from rocks or veins, are washed out by streams and mixed with alluvial deposits of sand or gravel, from which they can then be extracted by placer mining.
    2. (reef) A flat, shallow sandbank or reef submerged beneath the ocean surface, often with a sandy bottom suitable as an anchorage for seagoing vessels.

### plain

    Any broad, flat expanse of land that generally does not show significant variation in topography or elevation.

### plane table

    A small drawing board mounted on a tripod used in surveying, site mapping, and related disciplines to provide a solid and level surface upon which to make drawings, charts, and maps while in the field.

### planimetric map

    A map which uses a two-dimensional coordinate system, i.e. in which each point is represented by only two coordinates (x, y), as if all of the depicted features existed within a single, flat plane. These maps usually exclude information about vertical position and therefore do not show topographic relief and represent only horizontal distances.

### plat

    A cadastral map, drawn to scale, showing the legal boundaries and divisions of a surveyed tract of land, particularly of the type used to divide real property for sale and settlement in the Public Land Survey System of the United States.

### plate tectonics

    A geologic theory that the bending (folding) and breaking (faulting) of the solid surface of the Earth results from the slow movement of large sections of that surface called plates.

### plateau

    A large area of relatively flat terrain that is significantly higher in elevation than the surrounding landscape, often with one or more sides with steep slopes.

### platted land

    Land that has been divided into surveyed lots.

### playa

    An exceptionally flat, arid basin that is the dry bed of an evaporated lake; or the shallow, usually saline lake itself which periodically forms when the basin is temporarily covered with water, e.g. after substantial rainfall. See also salt pan.

### plucking

    An erosional phenomenon whereby a glacier gradually scours and displaces pieces of rock from the bedrock beneath it and transports them along with the glacial flow of ice and debris. As the glacier moves down a valley, friction causes the basal ice to melt and infiltrate joints and cracks in the bedrock; repeated freezing and thawing widens and deepens these cracks, eventually loosening the rock and causing large blocks and boulders to be carried along by the overlying ice. These boulders are often deposited hundreds of kilometers from their source, becoming erratics. The term is also sometimes used to describe the similar process of quarrying, which occurs on a smaller scale in fast-moving rivers and streams.

### plug

    A cylindrical mass of volcanic rock marking the neck of an ancient volcano, especially one exposed by denudation of the surrounding cone.

### plumb line

    A vertical reference line created by suspending a weight, known as a plumb bob or plummet, from a string above the Earth's surface and allowing it to hang freely in the direction of the pull of gravity. A precursor to the spirit level, plumb lines are used to establish a vertical datum in a wide range of applications, particularly in surveying to determine the nadir of a point in space, and often in combination with an instrument in order to set the instrument precisely over a fixed survey marker.

### plunge pool

    A deep depression at the base of a waterfall into which the water drops with great force, plucking and abrading the rock beneath and behind the falls and creating an often nearly circular concavity which may remain filled with water long after the waterfall itself dries up.

### plural society

    A situation in which two or more culture groups occupy the same territory but maintain their separate cultural identities.

### point bar

    A depositional feature made of alluvium that accumulates on the inside bend of a meandering stream or river, below the slip-off slope and often directly opposite a cut bank. Point bars are usually crescent-shaped beaches of sand, silt, or gravel, similar to shoals and river islands.

### polar aspect

    A planar map projection with its origin located at either the North or the South geographic pole.

### polar circle

    Either of the two circles of latitude enclosing the Earth's polar regions: the Arctic Circle in the Northern Hemisphere and the Antarctic Circle in the Southern Hemisphere.

### polar ice cap

    Either of the two very large regions near the Earth's geographical poles that are seasonally or persistently covered in ice, which occurs because high-latitude regions receive less direct solar radiation than other regions and therefore experience much lower surface temperatures. The Earth's polar ice may cover both land and sea, and varies in size seasonally and with long-term climate change. They typically cover a much larger area than true ice caps and are more correctly termed ice sheets.

### polar region

    Either of the two high-latitude regions surrounding the Earth's geographical poles (the North and South Poles), which are characterized by frigid climates and extensive polar ice caps. The polar region of the Northern Hemisphere is often simply called the Arctic and that of the Southern Hemisphere is called the Antarctic.

### polder

    A low-lying tract of land enclosed by dikes, forming an artificial hydrological entity by creating land from a naturally inundated area, e.g. by reclaiming land from a lake or sea, or by building barriers around a floodplain or marsh and then draining it. All polders are eventually below the surrounding water table some or all of the time, making them especially prone to flooding, and they often require continuous draining.

### pole

    1. An extreme geographical point, especially one of a pair.
    2. Either of the two points where the Earth's axis of rotation meets its surface, i.e. the geographic poles, representing the northern and southern extremities of terrestrial latitude: the Geographic North Pole and the Geographic South Pole.
    3. Either of the two ends of the geomagnetic field generated by the dynamo in the Earth's core. These ends may refer either to the true magnetic poles, known as the Magnetic North Pole and the Magnetic South Pole, which are not directly opposite each other, or to the antipodal poles of a hypothetical perfect dipole passing through the Earth's center, known as the Geomagnetic North Pole and the Geomagnetic South Pole.

### pole of inaccessibility

    A location that, with respect to a given geographical criterion, is the most difficult to reach according to that criterion, e.g. the geographical location that is the most distant from the nearest point meeting that criterion. The term most commonly refers to the so-called continental or oceanic poles of inaccessibility, i.e. the point on a given continental landmass that is the furthest distance from a coastline, and the point in the ocean that is the furthest distance from land, respectively.

### political geography

    The study of both the spatially uneven outcomes of political processes and the ways in which political processes are themselves affected by spatial structures. A sub-discipline of human geography, its primary concerns can be summarized as the relationships between people, state, and territory.

### polje

    A very large plain found in karstic regions, enclosed within a depression, usually elliptical, with a flat floor either of bare limestone or covered by alluvium, and generally surrounded by steep limestone walls; or more broadly any enclosed or nearly enclosed valley. The term is used primarily in the Slavic-speaking world.

### polynodal

    Many-centered; having many nodes.

### polynya

    An area of unfrozen seawater surrounded by an otherwise contiguous area of pack ice or fast ice. Polynyas are often formed along polar coastlines through the action of katabatic winds, but may also form in the open ocean.

### pond

    A natural or artificial body of standing water that is usually smaller than a lake.

### populated place

    A place or area with clustered or scattered buildings and a permanent human population (a city, settlement, town, or village) that is referenced with geographic coordinates.

### population

    A collection of organisms of the same group or species which live in a particular geographical area. In the context of geography, it often refers to a collection of humans and is represented at the most basic level as the number of people in a given geographically or politically defined space, such as a city, town, region, country, or the entire world.

### population geography

    A branch of human geography that studies the ways in which spatial variations in the composition, distribution, migration, and growth of populations are related to the nature of places. This often involves factors such as where populations are found and how the size and composition of these populations is regulated by the demographic processes of fertility, mortality, and migration.

### positioning system

    Any technology or mechanism used to determine the position of an object in space. Numerous methods for determining position have been practiced since ancient times, though modern positioning systems generally rely on electromagnetic and/or satellite-based technologies capable of providing coverage ranging from local or regional to global and accuracy ranging from tens of metres to sub-millimetre.

### post-industrial

    An economy that gains its basic character from economic activities developed primarily after manufacturing grew to predominance. Most notable would be quaternary economic patterns.

### potamology

    The branch of hydrology that studies rivers, including the processes and phenomena that occur at their sources, main channels, and mouths; the structure and morphology of drainage basins; and the water, thermal, ice, and sediment regimes that affect and are affected by river discharge.

### potentiometric surface

    See piezometric surface.

### pothole

    1. Any smooth, bowl-shaped or cylindrical hollow, generally deeper than it is wide, that is carved into the rocky bed of a watercourse such as a stream or river. Fluvial potholes are created by the grinding action of stones or coarse sediment kept in perpetual motion in the same spot by the turbulence of the current. The term is also used to refer to plunge pools beneath waterfalls, which are created by similar processes. See also kolk.
    2. A vertical or steeply inclined karstic shaft in a limestone deposit.
    3. In the Great Plains of North America, a shallow depression, generally less than 10 acres (4.0 ha) in area, occurring between dunes or on morainic relief on a prairie and often filled by an intermittent pond or marsh.
    4. Another name for a kettle.
    5. Another name for a panhole.

### prairie

    A type of temperate grassland ecosystem dominated by a characteristic composition of grasses, herbs, and shrubs, rather than by trees. The term is used primarily in North America, but similar ecosystems can be found across the world.

### Precambrian rock

    The oldest rocks, generally more than 600 million years old.

### presque-isle

    A peninsula connected to the mainland by an extremely narrow neck of land such that the land at its distal end is very close to being an island. See also tied island.

### prevailing winds

    The direction from which winds most frequently blow at a specific geographic location.

### primary sector

    That portion of a region's economy devoted to the extraction of basic materials (e.g., mining, lumbering, agriculture).

### Prime Meridian

    The imaginary line running from north to south through the Royal Observatory in Greenwich, England which is assigned a longitude of 0 degrees and is therefore used as the reference point for all other lines of longitude.

### proglacial

    Preceding, in advance of, or in front of the toe or moraine of a glacier, either spatially or temporally.

### progradation

    The natural extension of a shoreline into a body of water by the gradual accumulation of sediment over time, especially as a result of fluvial sedimentation processes, such as the protrusion of a river delta into the sea. This occurs when the volume of sediment carried by the river and deposited at its mouth exceeds the volume lost through subsidence, sea level rise, or coastal erosion.

### prominence

    1. A conspicuous high point that projects above or beyond its surroundings, e.g. a butte or a promontory.
    2. An abbreviation of topographic prominence.

### promontory

    A raised mass of land that projects into a lowland or a body of water. Compare headland and cape.

### protected area

    Any clearly defined geographic space in which human occupation or the exploitation of resources is limited or forbidden through legal or other effective means because of the area's recognized natural, ecological, cultural, or historical value.

### province

    A type of second-level administrative division within a country or federal state.

### public land

    Any land area held and managed in the public domain by a federal or local government.

### pueblo

    A type of Indian village constructed by some tribes in the southwestern United States. A large community dwelling, divided into many rooms, up to five stories high, and usually made of adobe. This is also a Spanish word for town or village.

### puna

    An ecoregion in the central Andes Mountains of South America, or any of the various high-altitude ecosystems encompassing it, including cold deserts and alpine grasslands.
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## Q

### quadrangle

    A standard division of the Earth's surface area used in maps produced by the United States Geological Survey. Quadrangles are four-sided polygons of varying size, depending on the map series; for example, 7.5-minute quadrangles divide the mapped surface into quadrilaterals measuring 7.5 minutes (0.125 degrees) of latitude by 7.5 minutes of longitude, with each 7.5-minute map showing the topographical detail within one particular quadrilateral of this size. Because the boundaries of quadrangles are based on lines of latitude and longitude, the northern and southern limits of a quadrangle map are not straight lines, and the eastern and western limits are usually not parallel; the actual surface area covered by each map varies with the latitudes depicted.

### quagmire

    See bog.

### quarry

    A place from which stone, rock, sand, gravel, slate, or aggregate is excavated from the ground, especially a large man-made pit that is exposed to the open air.

## R

### raft ice

    A jumbled mass of blocks of ice that impedes the flow of water in a river or stream.

### rail gauge

    The distance between the two rails of a railroad.

### railroad bed

    The track or trace of a railroad route, commonly raised slightly above the adjacent natural ground surface and constructed mostly of locally occurring, earthy materials (e.g. gravel and rock fragments).

### rain shadow

    An area on the leeward (downwind) side of a mountain or mountain range that receives greatly diminished precipitation.

### rainforest

    Any forest characterized by abundant rainfall, dense layers of vegetation, and extremely high biodiversity. Rainforests are found in both tropical and temperate regions. The term jungle is sometimes used to refer to a tropical rainforest.

### rake

    A sloping terrace on a mountainside or rock face. The term is used primarily in Scotland.

### raster

    A representation of spatial data within a two-dimensional image that defines space as a rectangular array or grid of equally sized cells arranged in rows and columns, where each cell can be identified with location coordinates and is associated with attribute values containing a discrete amount of information from one or more layers or "bands". Raster models are useful for storing and presenting large amounts of complex multivariate data that vary continuously across space, as is commonly encountered in maps, aerial photographs, satellite imagery, and many other aspects of geographic information science. Raster data are contrasted with vector data, which instead store and represent geographic information in the form of points, lines, and polygons.

### ravine

    A fluvial slope landform of relatively steep sides, sometimes with an intermittent stream flowing along the downslope channel. Ravines are typically narrower and shallower than canyons, larger than gullies, and smaller than valleys.

### re-entrant

    See draw.

### reclaimed land

    1. Any land area that is artificially created from earthy fill material that has been intentionally placed and shaped so as to approximate natural contours, especially as part of land reclamation efforts such as those designed to bury tailings following the cessation of mining operations.
    2. An area of land, commonly submerged underwater in its natural state, that has been protected by artificial structures such as dikes and drained for agricultural or other purposes (e.g. a polder).

### reef

    A submerged ridge-like or mound-like structure built by sedentary calcareous organisms, especially corals, in shallow marine waters, and consisting primarily of their skeletal remains, though often still supporting living colonies as well. Reefs may also be partially composed of rocks, sand, gravel, or seashells. They are locally prominent above surrounding sediments deposited on the sea floor, rising to or nearly to the water's surface.

### reference ellipsoid

    A mathematically defined surface that approximates the geoid for use in spatial reference systems or geodetic datum definitions. Because of their relative simplicity, reference ellipsoids are used in geographic applications as preferred surfaces on which geodetic network computations are performed and point coordinates such as latitude, longitude, and elevation are defined.

### reg

    See desert pavement.

### region

    An area having some characteristic or characteristics that distinguish it from other areas; a territory that is of interest to people, for which one or more distinctive traits (e.g. climate, economy, history, etc.) define its identity.

### regionalism

    1. The feeling or expression of a common sense of identity, purpose, or group consciousness associated with a particular geographical region, e.g. the Southern United States, Scandinavia, or Lower Egypt, often combined with the creation of institutions that accommodate that particular identity and shape public action.
    2. A movement to decentralize central government, placing administrative responsibility instead at a level intermediate between that of the state and that of smaller local or municipal units.
    3. In architecture, an approach that strives to counter placelessness and lack of identity by incorporating elements of the building's geographical context in its design.

### regiopolis

    A city located outside the core of a metropolitan area that serves as an independent driving force for political, economic, or cultural development within a larger region. Contrast metropolis.

### regolith

    A layer of loose, unconsolidated, heterogeneous superficial deposits (e.g. soil, sediments, broken rock, volcanic ash, wind-blown material, etc.) overlying solid bedrock.

### relative height

    See topographic prominence.

### relative relief

    The elevation or altitude of one location relative to another location; the difference between the highest and lowest points within a given geographical area.

### relief

    See terrain.

### relief map

    See topographic map.

### remote

    (of a particular location) Isolated or inaccessible, either by being physically very distant from another location or by lacking connectivity to transportation or communication networks which would otherwise make exchange between locations convenient.

### remote sensing

    The gathering of information about an object or place from a remote location (i.e. without making physical on-site observations), most commonly by the use of satellite- or aircraft-based electromagnetic sensor technologies.

### representative fraction (RF)

    The fraction expressing the ratio between the distance measured between two points on a map and the corresponding actual distance measured between those points in the real world, used to indicate the map's scale. The fraction's numerator is typically 1 (indicating one of some specified unit of length, e.g. inches or centimetres) and the denominator is the number of the same unit in the real world which this length represents on the map. For example, a representative fraction of 1⁄1,000,000, often written as 1:1,000,000 or 1:1 mn, means that one inch (or one centimetre) on the map itself is equivalent to one million inches (or centimetres) in the real world. One statute mile is equal to 63,360 inches, so 1,000,000 inches is approximately 16 miles.

### reservoir

    An artificial lake or an artificially enlarged natural lake that is used to store water. Reservoirs are often created by the construction of a dam or lock in a natural drainage basin.

### resource

    Anything that is both naturally occurring and of use to humans.

### rhumb line

    A line drawn on the surface of a sphere (or on an idealized representation of the Earth) which crosses all meridians of longitude at the same angle, and which therefore has constant bearing relative to true or magnetic north.

### ria

    The seaward end of a river valley which has been flooded as a result of a rise in sea level.

### ribbon development

    The build-up of residential and economic communities along the main routes of communication and transportation radiating from a city or other developed area, because of the advantages of accessibility, relatively inexpensive land, and trade from passers-by.

### ribbon lake

    A long, narrow, finger-shaped lake, especially one found in a glacial trough and dammed by a rock bar or moraine.

### ridge

    An elongated raised landform which forms a continuous elevated crest for some distance, such as a chain of hills or mountains. The line formed by the highest points, with only lower terrain immediately to either side, is called the ridgeline.

### riegel

    An outcrop of resistant bedrock that forms a bar across a glacial trough and often acts as a dam to impound the waters of a lake.

### rift valley

    A valley that has formed along a long, narrow continental trough bounded by normal faults; a graben of regional size.

### rimaye

    See bergschrund.

### riparian rights

    The rights of water use possessed by a person owning land containing or bordering a watercourse or lake.

### river

    A natural watercourse, usually fresh water, that flows towards an ocean, sea, lake, another river, or in some cases into the ground.

### river pocket

    An area of land enclosed within the bend of a river, especially where the bend is extended or pronounced (e.g. a meander) and the only road access is along the isthmus. The term is used primarily in Australia.

### riverine

    Located on or inhabiting the banks or the area adjacent to a river or lake. Compare riparian.

### road map

    Any map that shows the man-made roads, streets, highways, railways, and/or other transportation routes within the map's coverage area, especially one which specifically prioritizes the display of this information over other information such as geographic features. Road maps are usually designed to emphasize information relevant to motorists, often including political boundaries and labels as well as points of interest such as important buildings and businesses, tourist attractions, parks and recreational facilities, hotels, restaurants, gas stations, public transit networks (e.g. airports, train stations, etc.), and emergency services. The widths of the roads themselves are often exaggerated to make the routes more conspicuous.

### roadstead

    A body of water, natural or man-made, that is sheltered from rip currents, spring tides, and swells, and is therefore a known general station in which ships can safely be anchored without dragging or snatching.

### rock mill

    See pothole.

### rôche moutonnée

    See sheepback.

### route

    1. A way or course taken in getting from one place to another; an established or selected course of travel or action; a line of travel or means of access, especially when marked by a path, track, road, or rail.
    2. A circuit traveled in delivering, selling, or collecting goods, e.g. by a mail carrier.

### routefinding

    The determination of a viable route or line of travel between two places, especially in rugged or unexplored areas such as mountainous terrain or in conditions of poor visibility, and especially when done without the benefits of prior knowledge of the area, maps, or other technology that might aid orienteering, instead relying entirely on recognition of natural features and landmarks and quick estimations of distance, scale, ease, and safety.

### rural

    An adjective describing any geographic area located outside areas of significant human population such as towns and cities; all population, housing, and territory not included within an urban area is often said to be rural. Rural areas are typified by low population densities, very small settlements, and expansive areas of agricultural land or wilderness.
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## S

### saddle

    For a given pair of mountain summits, the region surrounding the elevational low point or col on the ridge connecting the two summits; mathematically, it is the critical point that is simultaneously a relative minimum in one axial direction (e.g. between the peaks) and a relative maximum in the perpendicular direction. Assuming it is navigable, a saddle can be thought of as the area surrounding the highest point on the lowest route which one could use to pass between the two summits.

### salient

    Any narrow, elongated protrusion of a larger territory, either physical or political, such as a state.

### salt marsh

    A natural coastal marsh ecosystem in the upper intertidal zone, between land and open seawater or brackish water, that is regularly flooded by the tide at high water. Salt marshes support dense stands of terrestrial salt-tolerant plants, especially grasses and low shrubs, which trap and bind sediments from the ocean and help protect the nearby shoreline from coastal erosion.

### salt pan

    A large, flat expanse of land naturally covered with salt and/or other minerals, usually to the exclusion of virtually all vegetation. Salt pans are common in deserts, where they form by the precipitation of dissolved mineral solids as a large body of water evaporates. See also playa.

### saltwater

    Any naturally occurring water, especially the water from a sea or ocean, characterized by high concentrations (between 3 and 5% by volume) of dissolved salts, primarily sodium and chloride ions, relative to fresh water or brackish water. Salt water in the Earth's oceans has an average salinity of about 3.5%; it is both denser and freezes at a lower temperature than fresh water.

### sand dune

    See dune.

### sand sea

    See erg.

### sandbar

    See shoal.

### sandur

    See outwash plain.

### satellite navigation

    A method of navigation or an autonomous geospatial positioning system that relies on artificial satellites in orbit around the Earth to transmit time signals at radio frequencies along a line of sight to electronic receivers on the surface, which can then use this information to determine their location, direction, and the current local time to high precision. Satnav systems operate independently of telephonic or internet connectivity, though simultaneous use of these technologies can enhance the accuracy and usefulness of the positioning information generated.

### satellite state

    A formally independent state or polity which nevertheless depends economically, politically, or militarily upon, or is strongly influenced or controlled by, another, more powerful state.

### savanna

    A mixed woodland-grassland ecosystem characterized by scattered trees and bushes that are sufficiently widely spaced that the canopy does not close, permitting enough sunlight to reach the ground to support an unbroken herbaceous layer of primarily xerophytic grasses. The term is used especially to refer to the vast, hot, arid grasslands covering parts of equatorial Africa, South America, and northern Australia, but is also sometimes applied more broadly.

### scale

    The relationship between a linear measurement on a map and the distance it represents on the Earth's surface.

### scarp

    A steep cliff face or slope terminating an elevated surface of low relief, formed either because of faulting or by the erosion of inclined rock strata.

### schrund

    See bergschrund.

### scroll

    1. A narrow stretch of floodplain added to the outer end and downstream side of spurs between enclosed meanders on a river.
    2. A type of point bar consisting of a low, narrow ridge running in line with the curve of a meander, formed when the river overflows its banks.

### sea

    1. Any large body of salt water surrounded in whole or in part by land.
    2. Any large subdivision of the World Ocean. "The sea" is the colloquial term for the entire interconnected system of salty bodies of water, including oceans, that covers the Earth.

### sea lane

    A navigable route across a wide waterway such as an ocean, sea, or large lake that is regularly used for maritime trade by large vessels or ships because it is safe, direct, and economical.

### sea level

    The average level of the surface of one or more of Earth's oceans from which heights such as elevation and altitude are commonly measured. Often called mean sea level (MSL), it is a type of standardized geodetic vertical datum that is used in numerous applications, including surveying, cartography, and navigation. Mean sea level is commonly defined as the midpoint between the mean low and mean high tides at a particular location.

### sea stack

    See stack.

### seabed

    The bottom of a sea or ocean. As with land terrain, the ocean floor may have ridges, mountains, valleys, and plains.

### seaboard

    Any extensive region of land adjacent to the sea, broadly synonymous with coast or coastline.

### seamount

    A mountain (often a volcano) rising from the ocean floor whose summit does not reach the water's surface and which is therefore entirely submerged and not an island or islet.

### search space

    In human geography, the locations within an area where an individual or group searches for the resources necessary to meet their specific needs (e.g. for housing or employment), based on information from their current awareness space.

### seaway

    See sea lane.

### second home

    A seasonally occupied dwelling that is not the primary residence of the owner. Such residences are usually found in areas with substantial opportunities for recreation or tourist activity.

### secondary-intercardinal directions

    The set of eight intermediate directions used in cartography and navigation, each of which is located halfway between a pair of intercardinal directions: north-northeast (NNE), east-northeast (ENE), east-southeast (ESE), south-southeast (SSE), south-southwest (SSW), west-southwest (WSW), west-northwest (WNW), and north-northwest (NNW). They may or may not be explicitly labeled on a compass rose.

### secondary sector

    That portion of a region's economy devoted to the processing of basic materials extracted by the primary sector.

### sector principle

    The principle on which political claims to territory in the polar regions have historically been made, such that the territories are divided into arbitrary wedge-shaped sectors, each one having an apex at the geographic pole and including outer areas of both land and sea extending to a particular latitude. Because of the limited accessibility and generally low material value of both the Arctic and Antarctic, the sector principle has emerged as a means of formally sharing responsibility for these regions between the world's sovereign states.

### sedimentary rock

    Rock formed by the hardening of material deposited in some process; most commonly sandstone, shale, and limestone.

### seismograph

    A scientific instrument that detects and records vibrations (seismic waves) produced by earthquakes.

### selva

    A dense equatorial forest, especially in the Amazon basin of South America.

### serac

    A large block or pillar of glacial ice formed by the intersection of numerous crevasses where the glacier fragments as it reaches a steep slope. Seracs are usually found in icefalls, often in large numbers, in mountainous terrain.

### settlement

    Any place where people live and form communities.

### shadow effect

    The phenomenon by which a large, well-served urban center affects the transport services of a nearby smaller town or city, often by drawing producers and consumers away from the smaller settlement and toward the larger one, causing the smaller settlement to be relatively ill-provided with direct services.

### shakehole

    See doline.

### shallows

    An area of water of relatively little depth, e.g. in a sea, lake, or river.

### sheepback

    A rock formation created by the passage of a glacier over underlying bedrock, which often results in asymmetrical erosional forms created by abrasion on the upstream side of the rock and plucking on the downstream side.

### shelf sea

    A relatively shallow marginal sea, generally less than 300 metres (980 ft) deep, beneath which a portion of a continental shelf is submerged.

### shield

    A broad area of very old rocks above sea level that is usually characterized by thin, poor soils and low population densities.

### shield volcano

    A class of volcano that resembles an inverted warrior's shield, with long gentle slopes produced by multiple eruptions of fluid lava flows.

### shoal

    A natural submerged ridge, bank, or bar that consists of or is covered by sand or other unconsolidated material and rises from the bed of a body of water to just below or above the surface.

### shore

    The fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. Compare coast.

### shore platform

    See wave-cut platform.

### shoulder drop

    See topographic prominence.

### sinkhole

    A crater formed when the roof of a cavern collapses, usually found in areas of limestone rock.

### site

    The features of a place related to the immediate environment on which the place is located (e.g. terrain, soil, subsurface, geology, groundwater, etc.).

### situation

    The features of a place related to its location relative to other places (e.g., accessibility, hinterland quality).

### skerry

    A small, rocky islet or reef, often one of a series lying just offshore and parallel to the main trend of the coastline, over which large waves may break at high tide or in stormy weather.

### slack

    A shallow hole or hollow among coastal sand dunes or mud banks.

### slack water

    The brief period of time during which a body of water susceptible to tides is completely unstressed because the tidal stream is almost still, i.e. there is no movement in either direction in the tidal current, usually the period immediately before and after the high and low water marks, prior to the tide reversing direction.

### slant range

    The line-of-sight distance along the relative direction between two points, especially two points which are not at the same elevation relative to a specific datum. If the two points are at the same elevation, the slant range equals the horizontal distance.

### slash

    1. In the southeastern United States, a low-lying swampy or boggy area, overgrown with shrubs and cane grasses and favorable for the growth of the slash pine and related trees.
    2. The debris of felled trees, especially in a forest that has been subjected to slash-and-burn agriculture.

### slide

    1. The noticeable track of bare rock or furrowed earth left by the mass movement of soil, mud, snow, or rock under shear stress down a steep slope, as in a landslide or avalanche.
    2. The mass of material moved or deposited by such an event, and which has become fixed or settled upon the landscape.

### slip-off slope

    The more gently sloping of the two banks of a river or stream, usually on the inside bend of a meander, as opposed to a cut bank.

### slope

    The upward or downward inclination of a natural or artificial surface (e.g. a hillside or a road), or the degree or nature of such an incline; a deviation from the perpendicular or horizontal direction (these directions generally being assigned with respect to the direction of the force of gravity). See also grade.

### slough

    A type of wetland – usually a swamp, a shallow lake, or a backwater branching from or feeding into a river – in which water tends to be stagnant or flows only very slowly on a seasonal basis.

### slum

    A residential settlement or neighborhood, usually in or near an urban area, characterized by densely packed and poorly built or dilapidated housing units such as shacks and a deterioration or lack of civic infrastructure such as reliable water, electricity, sanitation, law enforcement, and other basic services, and usually associated with extreme poverty and overpopulation.

### smog

    A mixture of particulate matter and chemical pollutants in the lower atmosphere, usually over urban areas.

### Standard Metropolitan Statistical Area (SMSA)

    A statistical unit of one or more counties that focus on one or more central cities larger than a specified size, or with a total population larger than a specified size. This is a reflection of urbanization.

### snout

    The lowermost margin or extremity of a glacier, always either gradually advancing or retreating, sometimes partially hidden by morainic material, and commonly featuring a cave from which meltwater flows.

### snowline

    The lowest elevation at which snow remains throughout the year if the summer warmth does not completely melt the winter accumulation, e.g. on a high mountain. This elevation varies widely with latitude, local climate, directional aspect, and steepness of slope, such that the snowline may be very different on different mountains in the same range, on different faces of the same mountain, or on the same face in different years.

### soil horizon

    A distinct layer of soil encountered in vertical section.

### solution pan

    See panhole.

### solubility

    The degree to which a substance can be dissolved in another substance; in a geographical context, the characteristic of soil minerals that leads them to be carried away in solution by water. See also leaching.

### sound

    1. A large inlet of a sea or ocean that is larger than a bay, deeper than a bight, and wider than a fjord.
    2. A narrow sea or ocean channel between two landmasses.

### South Geographic Pole

    The point in the Southern Hemisphere where the Earth's axis of rotation meets its surface. It is the southernmost point on Earth, directly opposite the North Geographic Pole, and is located on continental land in Antarctica at a latitude of 90 degrees South; its longitude can be assigned any degree value. See also South Magnetic Pole.

### South Geomagnetic Pole

    The point in the Southern Hemisphere where the axis of a theoretical simplified dipole passing through the center of the Earth would intersect the Earth's surface. It is antipodal to the North Geomagnetic Pole. Because of the fluid nature of the Earth's molten core, the true axis of the Earth's magnetic field is not a perfect dipole, and so the Geomagnetic Poles and the actual Magnetic Poles lie some distance apart.

### South Magnetic Pole

    The point in the Southern Hemisphere at which the Earth's magnetic field points vertically downward. It is close to but distinct from the Geographic South Pole and the Geomagnetic South Pole, and its precise location varies considerably over time due to frequent magnetic changes in the Earth's core. Its counterpart in the Northern Hemisphere is the North Magnetic Pole, though the two poles are not directly opposite each other.

### Southern Hemisphere

    The half sphere of the Earth that is south of the Equator. It is opposite the Northern Hemisphere.

### space economy

    The locational pattern of economic activities and their interconnecting linkages.

### spatial analysis

    1. Any of the wide variety of formal techniques used to study entities according to their topological, geometric, or geographic properties.
    2. An approach to geography in which the locational variations of a phenomenon or a series of phenomena are studied and the factors influencing or governing the observed patterns of distribution within space are investigated. This approach attempts to break down spatial patterns into simple elements so that measurements can be made of individual sub-patterns, which then allows the comparison of two or more distinct patterns and the development of statistical tests to determine whether a given pattern differs significantly from random variation.

### spatial citizenship

    The participation of individuals and groups of laypeople in decision-making about spatial planning and social rules in public spaces through the reflexive production and use of geographic media such as maps, virtual globes, and GIS software, particularly in order to question existing perspectives on the appropriation of space and the actions permitted within that space and to negotiate alternative spatial visions.

### spatial complementarity

    The occurrence of location pairing such that items demanded by one place can be supplied by another.

### spatial interaction

    Movement or exchange between locationally separate places.

### spatial reference system (SRS)

    A coordinate-based local, regional, or global system used to locate geographical entities and which defines a specific map projection as well as transformations between different systems.

### spit

    A type of bar or shoal extending from a beach into an ocean or lake and which develops by the deposition of sediment as a result of longshore drift. Spits form where the direction of the shoreline sharply changes direction, such as at a headland, and often develop a "hooked" or recurve shape at their distal ends.

### spot elevation

    A point on a map or chart whose height or elevation above a specified reference datum (often mean sea level) is explicitly annotated, usually by a numerical elevation value printed immediately adjacent to a dot or sawbuck indicating the point itself. Topographic maps often include spot elevations, wherever practicable, for the summits of hills, mountains, plateaus, and buttes; mountain passes; forks and intersections of roads, trails, and waterways; water surfaces of lakes and ponds; notable low points such as the local elevational minimum of a basin; very large flat areas; and any other point which may be of interest to the map user.

### spreading ridge

    See mid-ocean ridge.

### spring

    Any location where groundwater naturally emerges from an underground aquifer to the Earth's surface.

### spur

    A lateral ridge or other salient landform protruding from the side of a hill, mountain, or the main crest of a ridge and typically surrounded on at least three sides by steep hillsides.

### stack

    A coastal landform consisting of a steep and often vertical column or columns of rock above the surface of the sea and formed by erosion due to wave action.

### stage

    In hydrology, the height of the surface of a stream or river at a particular location and a particular point in time, with respect to a reference height such as its bed or a position on its banks, and used especially to monitor seasonal changes in discharge and flooding.

### stand

    An area of vegetation dominated by a single species, e.g. a stand of oak trees.

### state

    A compulsory political organization with a centralized government that maintains a monopoly of the legitimate use of force within a certain geographical territory. See country.

### steppe

    An ecoregion characterized by expansive grassland plains without trees apart from those near rivers and lakes.

### stopbank

    See levee.

### stoss

    An adjective describing the side of a hill or ridge that faces the direction from which an advancing glacier or ice sheet is moving or has moved; i.e. facing upstream or "up-ice" with respect to the glacier, and therefore most exposed to its abrasive action. The opposite side, facing downstream or away from the glacier, is known as the lee.

### strait

    See channel.

### strandline

    A beach or shoreline, especially a former or relict one, now elevated above the present water level, which appears as a bench or other visible demarcation lining the length of the shore at a common elevation. See also high water mark.

### strath

    A large river valley, typically wider and shallower than a glen. The term is used primarily in Scotland, Australia, and Canada.

### stratovolcano

    A steep-sided volcano built by lava flows and tephra deposits.

### stream

    A natural body of water in which surface water flows between the banks of a channel. Long, large streams are called rivers.

### stream order

    The hierarchical classification of all of the branching streams comprising a river system or watershed, usually by assigning an ordinal number to each individual tributary indicating the magnitude of its channel and/or its position within the overall drainage sequence. Several different numbering methods are in common usage. In the Strahler system, the outermost tributaries (i.e. near the sources) are designated first-order streams, and at least two streams of any given order must combine to form a stream of the next higher order, e.g. two first-order streams unite to form a second-order stream, two second-order streams join to form a third-order stream, and so on until the largest channel or main stem, terminating at the mouth, is reached.

### streambed

    The bottom of the channel of a stream or river, usually covered with rocks, sand, or debris and totally devoid of terrestrial vegetation if the stream has flowed recently. The bed is generally considered the part of the channel up to the normal water line, whereas the bank is the part above the water line.

### strip map

    A map covering only a narrow band of territory in which the user is interested, e.g. alongside each side of a trail or vehicle route.

### subcontinent

    A large landmass forming a contiguous part of an even larger continent, though often separable by physiographic or political boundaries, e.g. the Indian subcontinent; or a non-contiguous but still very large landmass that is smaller than one usually termed a continent, e.g. Greenland.

### subduction zone

    The place where two lithospheric plates come together, one riding over the other. Most volcanoes on land occur parallel to and inland from the boundary between the two plates.

### sublittoral

    1. Of or relating to the coastal area of the sea between the intertidal zone and the edge of the continental shelf. Compare littoral zone.
    2. Of or relating to the deepest parts of a lake or other large body of freshwater, distant from the shore, where plants cannot root. See also aphotic zone.

### subsequent

    (of a stream, river, or any natural water flow) Flowing along a course determined by the structure of the local bedrock. Contrast consequent and obsequent.

### suburban

    An adjective describing a mixed-use or residential area existing either as part of an urban area or as a separate community within commuting distance of a city; a place of this type is called a suburb. Suburbs are often defined by commuter infrastructures and have lower population densities than inner-city neighborhoods.

### suburbanization

    The process by which a human population shifts from urban to suburban residency, or the gradual increase in the proportion of people choosing to live in suburban neighborhoods which act as satellite communities within commuting distance of larger, centralized urban areas. Suburbanization is inversely related to urbanization.

### summit

    A point on a surface that is higher in elevation than all points immediately adjacent to it. Mathematically, it is a local maximum in elevation. The highest point of a hill or mountain is often referred to as the summit.

### surface water

    Water present on the surface of the Earth, such as in a river, lake, wetland, or ocean, as opposed to subsurface water.

### surveying

    The science, technique, and profession of determining the terrestrial or three-dimensional positions of points on the surface of the Earth and the distances and angles between them. These points are often used to draw maps and establish boundaries for property ownership, construction projects, and other purposes required by civil law.

### swale

    Any shallow channel or trough with gently sloping sides, either natural or artificial. Man-made swales are often designed to manage surface runoff and increase rainwater infiltration.

### swallet

    See ponor.

### swamp

    A forested wetland, often occurring along a large river or on the shores of a large lake.

### swirlhole

    See pothole.

### syrt

    A denudational highland or elevated flatland in Russia and Central Asia; a kind of dissected plateau.
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## T

### tablemount

    See guyot.

### taiga

    A moist subarctic coniferous forest that begins where the tundra ends and is dominated by spruces and firs.

### tailings

    Waste materials left over after the mining and processing of ore, during which a valuable mineral or metal is extracted from the uneconomic fraction accompanying it; the latter plus any substances applied in the extraction process are then discarded, often in spoil piles or ponds near the mine, usually because it is prohibitively expensive or impossible to relocate, reuse, or otherwise destroy the discarded material. Mine tailings are distinct from overburden, which is displaced during mining but not processed, and are often nutrient-poor or toxic to living organisms, making it difficult for plant and animal life to reclaim the environs without further treatment.

### talik

    A layer of year-round unfrozen ground between or within layers of permafrost, or between the active layer and permafrost.

### talus

    Loose, broken rock fragments of any size and shape, usually coarse and angular, derived from and lying at the base of a cliff or a very steep rock slope. Large quantities tend to accumulate on the slopes of high mountains by falling, rolling, or sliding from an eroding rockfall source. Compare scree.

### talweg

    See thalweg.

### tank

    A small man-made pond or reservoir made by impounding a stream or by constructing a pit or basin to collect and hold rainwater or snowmelt. Less commonly, the term may also refer to a natural pond or basin.

### tarn

    A mountain lake or pool of water formed in a cirque excavated by a glacier. A moraine may form a natural dam below a tarn.

### temperate zone

    Traditionally, either of the two midlatitude regions of the Earth defined by their latitudinal position between the tropics and the polar zones, i.e. the region between latitudes 23°30' N and 66°30' N, or that between 23°30' S and 66°30' S. In modern usage, the term may refer instead to regions of mild or temperate climate, regardless of latitude.

### temperature inversion

    An increase in temperature with height above the Earth's surface, a reversal of the normal pattern.

### tephra

    Solid material of all sizes explosively ejected from a volcano into the atmosphere.

### terminal moraine

    A moraine that forms at the terminus or snout of a glacier, marking its furthest advance. Debris transported by plucking and abrasion accumulates at the glacier's leading edge, where it is deposited in an unsorted pile of sediment as the ice begins to retreat.

### terracette

    One of a series of regularly spaced, horizontal, step-like ridges forming a distinctive ribbed pattern on a steep and usually grassy hillside, similar to an agricultural terrace or lynchet but naturally occurring. Various explanations for their origins have been suggested, including soil creep, solifluction, and animal trampling.

### terrain

    The vertical and horizontal dimensions of a land surface, usually as expressed in terms of elevation, slope, and orientation of geographical features.

### terrestrial

    1. Consisting of, living on, or relating to land, as opposed to water or air; e.g. a terrestrial animal lives primarily on land surfaces rather than in the sea.
    2. On, of, or relating to the Earth, as opposed to other planets or to celestial phenomena occurring outside the Earth's atmosphere.

### territorial waters

    1. A concept of the Law of the Sea defined as a belt of coastal waters extending at most 12 nautical miles (22 km) from the designated baseline (usually defined as the mean low-water line) for a coastal state and regarded as the sovereign territory of the state.
    2. Any area of water over which a state has legal jurisdiction, including internal waters, the exclusive economic zone, and potentially others.

### territory

    A specific area or portion of the Earth's surface, especially one claimed or administered by a particular country; similar to though distinct from a region.

### tertiary sector

    That portion of a region's economy devoted to service activities (e.g., retail and wholesale operations, transportation, insurance).

### thalweg

    The line of lowest elevation within a valley or watercourse, i.e. the line defining the longitudinal profile of an area with respect to the path followed by water draining from the area. Thalwegs may acquire special significance in political geography because disputed borders along rivers are often defined by the river's thalweg. This has sometimes led to conflict because the thalweg may change naturally over time.

### thaw lake

    A shallow, rounded lake or pond occupying a depression resulting from the melting of ground ice or permafrost, ubiquitous in thermokarst regions wherever there are flat lowlands with silty alluvium and high ice content, including much of the North American and Siberian Arctic. Many thaw lakes develop elongate shapes oriented with the long axis at a right angle to the prevailing wind.

### theodolite

    An optical instrument consisting of a small telescope, a spirit level, and graduated arcs mounted on a tripod, used in surveying and other applications to precisely measure angles between designated visible points in the horizontal and vertical planes.

### thermal spring

    See hot spring.

### thermal stratification

    The tendency of bodies of water such as lakes to separate into distinct thermal layers along a vertical gradient, such that water temperature varies predictably with increasing depth. Stratification is typically a seasonal phenomenon, as exemplified by deep lakes at temperate latitudes during the summer, which often form a warm, turbulent upper layer near the surface; a colder, denser bottom layer; and a transition zone of rapidly decreasing temperature in between. In all but the deepest lakes and oceans, these layers often disappear entirely in the spring and fall, when convective mixing makes the temperature more or less uniform at all depths, and may even invert if the surface freezes during the winter. Local topography, wind patterns, and dissolved solutes also strongly influence the formation and disruption of stratified waters.

### thermocline

    A thin layer of water in an ocean or lake, typically between the non-circulating hypolimnion and the warmer epilimnion, through which temperature changes more drastically with depth than it does in the layers above or below; e.g. temperature may decrease much more rapidly with increasing depth in this layer, commonly exceeding 1 °C (1.8 °F) per metre of descent.

### thermokarst

    A type of terrain characterized by expansive landscapes of small hummocks interspersed with irregular, marshy depressions formed by the thawing of ice-rich permafrost. The unique landforms of thermokarst, including pingoes, palsen, thaw lakes, alases, and linear and polygonal troughs, result from various periglacial and thermo-erosional phenomena common in the Arctic and on a smaller scale in mountainous areas such as the Himalayas and the Alps.

### tholoid

    A volcanic cone occurring inside of a larger volcanic crater or caldera.

### throw

    The vertical displacement of strata or rocks across the line of a fault, varying from a few millimetres to hundreds of metres in height. Those rocks on the higher side of the fault are termed upthrow, while those on the lower side are termed downthrow.

### tidal flat

    An extensive, nearly horizontal, barren or sparsely vegetated tract of land at the edge of a sea or ocean that is alternately covered and uncovered by the tide.

### tidal prism

    The total volume of water that flows in and out of a coastal inlet or estuary with each cycle of the tides, excluding any freshwater discharges; i.e. the difference in the inlet's volume between the mean high and low tides.

### tidal range

    The difference in height between high tide and low tide at a given location. This range may vary over the course of the year, e.g. during neap tides and spring tides.

### tide

    The periodic rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the Earth's rotation.

### tide pool

    A shallow pool of seawater, supplied regularly by incoming tides, that forms on a rocky intertidal shore.

### tied island

    An island that is connected to a mainland only by a narrow spit or tombolo which may or may not be occasionally submerged.

### till

    See glacial till.

### timberline

    See tree line.

### time distance

    A measure of how far apart places are in terms of the amount of time it takes to travel between them (how long does it take to travel from place A to place B?). This may be contrasted with other distance metrics such as geographic distance (how far is it?) and cost-distance (how much will it cost to get there?).

### time geography

    An interdisciplinary perspective, ontological framework, and visual language in which space and time are used as basic dimensions of analysis of dynamic processes and events, including social and ecological interactions, environmental changes, and biographies of individuals.

### time zone

    A region of the globe that observes a uniform standard time for legal, commercial, and social purposes. Most time zones span about 15 degrees of longitude, and in each of these divisions the mean solar time at an arbitrarily selected meridian (usually one near the longitudinal center of the division) is made the standard time across the entire zone. Time zones tend to follow political boundaries between countries and their subdivisions, however, rather than strictly following the same meridian, because it is convenient for areas in frequent communication to keep the same time.

### Tissot's indicatrix

    A mathematical contrivance used to illustrate the linear, angular, and areal distortions that result when projecting information from a curved three-dimensional geometric model such as a globe onto a two-dimensional map. A single indicatrix is traditionally a circle of determinate size drawn upon the surface of the globe, with center at specific coordinates; the extent to which this circle is deformed when the globe's coordinates are transformed onto a flat two-dimensional map makes apparent the nature of the distortion affecting nearby map features, such as the size and shape of landmasses, which might otherwise be difficult to visualize. Because distortion can vary greatly across a map, it is common for multiple indicatrices to be depicted at multiple points on the map, e.g. at major intersections of meridians and parallels.

### toe

    See snout.

### toll road

    A public or private road or highway for which a fee or toll is charged to drivers for passage.

### tombolo

    A sandy or shingle-covered spit, bar, or isthmus connecting an island to the mainland or to another island (thereby forming a tied island).

### topographic map

    A map that uses contour lines to represent the three-dimensional features of a landscape on a two-dimensional surface.

### topographical relief

    See terrain.

### topographic isolation

    The minimum great-circle distance between the summit of a mountain or hill and a point of equal elevation, representing a radius of dominance in which the summit is the highest point.

### topographic prominence

    A measure of the independence of a mountain or hill defined as the vertical distance between its summit and the lowest contour line completely encircling it but containing no higher summit within it; or, equivalently, the difference between the elevation of the summit and the elevation of the key col. Mountains with high prominence tend to be the highest points in their vicinity.

### topography

    The physical features of a place, or the study and depiction of physical features, both natural and man-made, including terrain relief.

### topology

    In geographical studies, a discipline concerned with the mathematical analysis of enclosure, order, connectivity, contiguity, and relative position rather than with actual distance and orientation. Topological relationships are commonly expressed in terms of networks and depicted with topological maps.

### topological map

    A type of diagrammatic map which depicts the actual positional relationships between certain features but on which true scale is distorted and unnecessary detail is absent in order to accommodate other considerations (e.g. simplicity so as to aid understanding of a complex communications network or public transit system).

### toponymy

    The study of placenames (known as toponyms), their origins, meanings, use, and typology.

### tor

    A prominent, free-standing rock outcrop that rises abruptly from the smooth slopes of a gently rounded hill or ridge. In the United Kingdom, the term is also used to refer to the hill itself.

### town

    A medium-sized human settlement that is generally larger than a village but smaller than a city, though the criteria for distinguishing a town vary considerably in different parts of the world.

### township and range

    The rectangular system of land subdivision used to plat real property for sale and settlement in much of the agriculturally settled United States west of the Appalachian Mountains, established by the Land Ordinance of 1785.

### towpath

    A road or path alongside a navigable river, canal, or other inland waterway designed to allow land vehicles, draught animals, or a team of human pullers to tow a boat or barge.

### trafficability

    The capacity of a soil or of a particular type of terrain to permit the movement of vehicles or pedestrians.

### transferability

    The extent to which a good or service can be moved from one location to another; the relative capacity for spatial interaction.

### transhumance

    The seasonal movement of people and animals in search of pasture. Commonly, winters are spent in snow-free lowlands and summers in the cooler uplands.

### transverse

    Crosswise; lying across; crossing from one side to another, as a line on a map.

### transverse coast

    See discordant coastline.

### transverse dune

    A sand dune with its crest oriented at right angles to the direction of the prevailing wind, as opposed to the orientation of a longitudinal dune.

### transverse valley

    A valley which cuts across a ridge or mountain range at right angles to the primary orientation of the crest. Contrast longitudinal valley.

### trap street

    In cartography, a misrepresented or nonexistent road or street that is deliberately included on a map (often outside the map's nominal area of coverage) for the purpose of detecting plagiarism by acting as a copyright trap: plagiarists who have copied other cartographers' work would find it difficult to explain the inclusion of the trap street on their map as coincidental. For this reason trap streets are often inconspicuous and given unique names. Many other map features are also used as copyright traps, including natural features and entire towns, and the implementation may also involve mislabeling features such as topographic elevations as well as making subtle stylistic alterations such as exaggerated or nonexistent bends in roads or rivers, ideally in a way that does not interfere significantly with navigation.

### traverse

    1. In surveying, a line or route and the sequence of points on it at which observations or measurements are made, or the process by which such a sequence is established. The term may also refer more generally to any route or path traveled for any purpose.
    2. A relatively horizontal route taken when the primary goal is to move vertically so as to bypass obstacles, as in rock climbing and mountaineering.

### tree line

    The latitudinal or elevational limit of normal tree growth. Beyond this limit (i.e. closer to the poles or at higher elevations) climatic conditions are too severe for such growth and trees are stunted or entirely absent. The term cold timberline may also be used to emphasize that the limiting factor is temperature, particularly when distinguishing it from the dry timberline of arid regions, where tree growth is instead limited by the availability of water.

### triangulation

    The process of determining the location of a given point or object, especially its distance from an observer, by measuring only the angles to it from two known points along a common baseline, which represent two vertices of an imaginary triangle. The unknown point can then be fixed as the third vertex of the triangle, using the one known side and two known angles. Triangulation differs from trilateration, which measures distances to the point directly instead of angles.

### tributary

    A stream or river that flows into a larger stream or main stem or a lake, rather than directly into a sea or ocean. Contrast distributary.

### tropic

    Either of the two parallels of latitude marking the boundary of the tropics: the Tropic of Cancer and the Tropic of Capricorn.

### Tropic of Cancer

    The northernmost circle of latitude on the Earth at which the Sun appears directly overhead at its culmination, which lies approximately 23.4 degrees north of the Equator. Its southern equivalent is the Tropic of Capricorn.

### Tropic of Capricorn

    The southernmost circle of latitude on the Earth at which the Sun appears directly overhead at its culmination, which lies approximately 23.4 degrees south of the Equator. Its northern equivalent is the Tropic of Cancer.

### tropical

    Characteristic of, located in, or relating to the tropics, either the specific parallels of latitude or the zone lying between those two parallels.

### tropics

    The region of the Earth's surface surrounding the Equator and bounded by the Tropic of Cancer (23.4° N latitude) and the Tropic of Capricorn (23.4° S latitude). It is characterized by high annual precipitation and the absence of any significant seasonal variation in temperature. The term is often used more broadly to describe any area possessing what is considered a hot, humid climate, regardless of latitude. See also temperate zone and polar zone.

### trough

    Any elongated, generally U-shaped valley, ravine, basin, or trench, natural or artificial, dry or wet. Particularly common usages refer to a submarine trench or deep in the ocean floor, or to a geological syncline.

### true north

    The direction along the Earth's surface towards the Geographic North Pole. Geodetic true north differs from magnetic north and grid north, and also very slightly from astronomical true north, which is based on the direction of the north celestial pole.

### true south

    The direction along the Earth's surface that is exactly opposite (i.e. bearing 180 degrees) of true north, towards the Geographic South Pole.

### trunk

    See main stem.

### tundra

    A treeless plain characteristic of the Arctic and subarctic regions.

### turlough

    In western Ireland, a depression or sinkhole which fills with water when the water table rises, e.g. by tidal effects.

### turnpike

    See toll road.
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## U

### umland

    An area which is culturally, economically, and politically related to a particular town or city.

### underfit stream

    A misfit stream that is seemingly too small to have eroded the valley or passage through which it flows, often an indication that there was once a larger stream in its place. Contrast overfit stream.

### underpopulation

    Economically, a situation in which an increase in the size of the labor force will result in an increase in per-worker productivity.

### uniform region

    A territory with one or more features present throughout which are absent or unimportant elsewhere.

### uninverted relief

    Topographic surface relief which closely reflects the shape and orientation of the underlying geological structure, i.e. where hills and ridges coincide with anticlines and valleys with synclines. Contrast inverted relief.

### upland

    Any area of land that is higher in elevation relative to another area, especially one that is populated by low hills or situated atop a plateau. The term is often used as a conditional descriptor to distinguish related habitats or ecosystems, especially freshwater riparian areas, on the basis of elevation above sea level. Upland areas are usually characterized by relatively fast-flowing waterways and hilly or rocky terrain. Contrast lowland.

### urban

    An adjective describing a settlement with a high population density and a developed infrastructure of built environment; places of this type are variously categorized as cities, towns, or conurbations, or simply called urban areas. Contrast suburban, exurban, and rural.

### urban geography

    The sub-discipline of geography that derives from the study of cities, urban processes, and the built environment.

### urban sprawl

    The unrestricted growth of housing, commercial development, and roads (typically of low densities) over large expanses of land, usually within or near an existing urban or suburban area and with little concern for civic planning. It is often considered a type of urbanization and almost always carries negative connotations.

### urban studies

    The study of the development of cities and urban areas, especially from historical, architectural, or civic planning perspectives.

### urbanization

    The process by which a human population shifts from rural to urban residency, the gradual increase in the proportion of people living in urban areas such as towns and cities, and the ways in which human societies respond and adapt to this change. Urbanization may be characterized as a specific condition at a set time (e.g. the proportion of the total population or physical area within a given set of towns or cities) or as an increase in that condition over time. It precipitates enormous social, economic, and environmental changes for the planet as a whole.

## V

### vale

    Another name for a valley.

### valley

    1. A low area between hills or mountains, often with a river running through it.
    2. A depression that is longer than it is wide.

### veld

    See bushveld.

### vent

    An opening at the Earth's surface through which volcanic materials (lava, tephra, and gases) erupt. Vents can be at a volcano's summit or on its slopes; they can be circular (craters) or linear (fissures).

### vertical exaggeration

    A scale used in certain maps, such as raised-relief maps, that deliberately distorts the apparent elevation of the map's topography in order to emphasize vertical features, which might otherwise appear too small to identify relative to the corresponding horizontal scale.

### viewshed

    The geographical area that is visible from a particular location. It includes all surrounding points within line-of-sight of the location and excludes points beyond the horizon or obstructed by terrain and natural or artificial objects.

### village

    A small, clustered human settlement or community, usually larger than a hamlet but smaller than a town and often in rural areas, though the criteria for distinguishing a village can vary considerably in different parts of the world.

### virtual globe

    A computer-generated three-dimensional software model or representation of Earth or another planet, providing the user with the ability to freely move around in the virtual environment by changing the viewing angle and position, and also to map many different types of data upon the surface of the Earth, such as land use statistics, meteorological records, and demographic quantities. An example is Google Earth.

### volcanic avalanche

    A large, chaotic mass of soil, rock, and volcanic debris moving swiftly down the slopes of a volcano. Volcanic avalanches can also occur without an eruption due to an earthquake, heavy rainfall, or unstable soil, rock, and volcanic debris.

### volcanic crater

    A type of crater created by volcanic activity, typically shaped like a bowl and containing one or more volcanic vents. Compare caldera.

### volcano

    A vent (opening) in the Earth's surface through which magma erupts, or the landform that is constructed by eruptive material.

### vrtače

    See doline.
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## W

### wadi

    1. A dry, ephemeral riverbed which contains water only when heavy rainfall occurs.
    2. Another name for a valley, used primarily in Arabic-speaking parts of the world.

### warping

    1. The slow, gentle deformation of the Earth's crust over a wide area, resulting in a raising or lowering of the surface.
    2. (sedimentation) Any process, natural or artificial, whereby the low-lying land of a tidal estuary is flooded, leading to deposition of silt, mud, or clay.

### wash

    1. The surging movement of the sea or any other large body of water; another name for the swash of a breaking wave.
    2. An area of sand and mud submerged or wettened during high tide and exposed during low tide.
    3. A dry streambed or gully; an arroyo.
    4. The collection of fine, granular material that is moved down a slope by erosional processes. See also wash slope.

### wash slope

    See gravity slope.

### waste land

    1. Wild, uncultivated, uninhabited land, especially that which is barren or desolate, supporting little or no plant and animal life, such as is found in some deserts.
    2. Land that yields little or no return when used for agriculture.
    3. Any land, common or otherwise, that was previously cultivated or developed but is now abandoned, and for which further use has yet to be found. See also brownfield land.

### water column

    In hydrology and oceanography, a conceptual column of water extending from the surface of an ocean, lake, or river to the sediment of the floor or bed, used to aid interpretation of properties and processes that vary along a depth gradient.

### water gap

    A low point or opening in a ridge or mountain range carved by the erosional activity of flowing water and through which water continues to flow in the present day. Contrast wind gap.

### water mapping

    The collection and presentation of point data related to the distribution, status, and sustainability of water supplies, generally by overlaying these data on a map showing administrative boundaries and population data, which can help to visualize and predict coverage issues and inform water management practices.

### water pollution

    The contamination of water by chemical or biological constituents which make it unfit for use.

### water table

    The level below the land surface at which subsurface material such as permeable rock is fully saturated with water. Where the water table is below the land surface, its depth reflects the minimum level to which wells must be drilled for groundwater extraction; a spring occurs where it reaches the land surface, and a permanent marsh or lake results where the theoretical water table is above the land surface. The level of the water table is the boundary between the vadose zone and the phreatic zone. Its depth fluctuates seasonally, which accounts for the intermittent flow of bournes. In some circumstances, there may be no regular water table; in others, a perched water table may exist.

### water-meadow

    A low-lying area of grassland beside a natural stream or river, subjected to periodic flooding through controlled irrigation in order to increase agricultural productivity, typically via a series of man-made canals or drains connected to the stream or river.

### waterbody

    See body of water.

### watercourse

    Any channel followed by a flowing body of water such as a river or stream, potentially including channels that are dry for part or all of the year.

### waterfall

    An abrupt and steep or perpendicular descent in a watercourse, e.g. in the bed of a river, resulting in a significant volume of water tumbling vertically downward or even freely falling by the pull of gravity. Waterfalls occur where the water's normally more level flow is interrupted by a nearly horizontal layer of hard rock overlying more easily eroded soft rock, or by the sharp edge of a plateau, or by the steep rock faces of a hanging valley, coastal cliff, or any other escarpment or knickpoint. They may be permanent or ephemeral; many alpine waterfalls form seasonally on mountainsides as snow and ice melts during the summer.

### waterhole

    A hollow or depression in the ground, natural or artificial, in which water can collect, either from precipitation or fed by a spring, especially in savannas or deserts where water is otherwise scarce; or a pool in the bed of an intermittent stream. Waterholes may be permanent or ephemeral.

### watershed

    Another name for a drainage divide, or for the entire catchment area of a drainage basin.

### waterway

    Any body of water that is deep, wide, and slow enough to be navigable by watercraft.

### wave-cut platform

    A flat erosion surface along the shore of a lake, bay, or sea that is formed by the undercutting and eventual collapse of a sea cliff as a result of repetitive wave action.

### weathering

    The breaking of rocks into smaller rocks, gradually becoming soil.

### weir

    A man-made obstruction built across the width of a river that alters its flow and usually results in a change in the height of the river level, commonly by permitting water to flow freely over a low barrier before cascading down to a lower level. Weirs may serve many purposes, including decreasing or increasing the force of the current, maintaining water depth, or diverting or impounding flow, typically for navigation, irrigation, fishing, to generate a head for a water mill, or to control outflow from a lake or reservoir. Compare dam and barrage.

### welfare geography

    An approach in human geography which considers the areal differentiation and spatial organization of human activity from the perspective of the welfare (health, prosperity, well-being, etc.) of the people involved, covering everything, positive or negative, contributing to the quality of human life and examining how and where observed inequalities between different societies arise.

### well

    A hole or shaft dug into the ground in order to access liquid resources, especially water, oil, or gas, from beneath the Earth's surface. Water wells typically tap into natural groundwater aquifers and remain filled with water up to the level of the water table, which can vary seasonally. The water is drawn up by a pump, or by using containers such as buckets that are raised mechanically or by hand. An artesian well taps a water source held under considerable pressure.

### Western Hemisphere

    The half sphere of the Earth that is west of the Prime Meridian and east of the antimeridian, and opposite the Eastern Hemisphere. The Western Hemisphere includes all of the Americas, the Atlantic Ocean, and a large portion of the Pacific Ocean.

### wilderness

    Any natural environment which has not been significantly developed or modified by human activity, or within which natural processes operate without human interference. Such areas are considered important for the survival of wild plant and animal species as well as for maintaining biodiversity and ecological stability. Wildernesses are often protected areas.

### wind gap

    A pass, notch, or opening in a ridge or mountain range, originally carved by a watercourse flowing through it but which is now dry as a result of stream capture. Contrast water gap.

### wind rose

    See compass rose.

### windward

    The side of a landmass facing the direction from which the wind is blowing. Contrast leeward.

### world city

    See global city.

### World Geodetic System (WGS)

    A standard geographic coordinate system, spheroidal reference ellipsoid (for raw altitude data), and geoid (which defines the nominal sea level) used in cartography, geodesy, and satellite navigation applications worldwide. The latest revision, WGS84, is the standard coordinate system used by the Global Positioning System.

### world map

    A map of most or all of the surface of the Earth.

## Y

### yardang

    A streamlined protuberance carved from bedrock or any consolidated or semi-consolidated material by the dual action of wind abrasion and erosion, especially one found in a desert.

### yazoo

    A tributary stream that runs parallel to and within the floodplain of the main channel for a great distance before joining it. The eventual confluence is known as a belated or deferred junction. The term is used primarily in the United States.

## Z

### zeuge

    A tabular mass of rock that has become perched atop a pinnacle created by erosion (often aeolian) of the softer, underlying rock. See also hoodoo.

### zibar

    A type of low sand dune with limited slip face development, often occurring in the corridors between higher dunes.

### zonation

    In biogeography and ecology, the separation of the Earth's flora and fauna into distinct groups occupying characteristic habitats, biomes, ecozones, or other idealized geographic divisions, primarily defined by climate, for the purpose of identifying and categorizing patterns in biodiversity. The boundaries of the resulting "zones" may be loosely defined or even somewhat arbitrary. The term has also been extended to include any ecological unit with spatial dimensions.

### zoning

    The public regulation of land and building use to control the character of a place.

### zenith

    The imaginary point on the celestial sphere that is directly above a particular location (i.e. in the vertical direction exactly opposite to the apparent direction of the gravitational force at that location). Contrast nadir.
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