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advanced function, requiring coordination with mapPlot() and
(possibly) also with mapAxis(), and so it is best avoided by
novices, who may be satisfied with the defaults used by
mapPlot()."><meta property="og:description" content="Plot longitude and latitude grid on an existing map. This is an
advanced function, requiring coordination with mapPlot() and
(possibly) also with mapAxis(), and so it is best avoided by
novices, who may be satisfied with the defaults used by
mapPlot()."></head><body>
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      <h1>Add a Longitude and Latitude Grid to an Existing Map</h1>
      <small class="dont-index">Source: <a href="https://github.com/dankelley/oce/blob/HEAD/R/map.R" class="external-link"><code>R/map.R</code></a></small>
      <div class="d-none name"><code>mapGrid.Rd</code></div>
    </div>

    <div class="ref-description section level2">
    <p>Plot longitude and latitude grid on an existing map. This is an
advanced function, requiring coordination with <code><a href="mapPlot.html">mapPlot()</a></code> and
(possibly) also with <code><a href="mapAxis.html">mapAxis()</a></code>, and so it is best avoided by
novices, who may be satisfied with the defaults used by
<code><a href="mapPlot.html">mapPlot()</a></code>.</p>
    </div>

    <div class="section level2">
    <h2 id="ref-usage">Usage<a class="anchor" aria-label="anchor" href="#ref-usage"></a></h2>
    <div class="sourceCode"><pre class="sourceCode r"><code><span><span class="fu">mapGrid</span><span class="op">(</span></span>
<span>  dlongitude <span class="op">=</span> <span class="fl">15</span>,</span>
<span>  dlatitude <span class="op">=</span> <span class="fl">15</span>,</span>
<span>  <span class="va">longitude</span>,</span>
<span>  <span class="va">latitude</span>,</span>
<span>  col <span class="op">=</span> <span class="st">"darkgray"</span>,</span>
<span>  lty <span class="op">=</span> <span class="st">"solid"</span>,</span>
<span>  lwd <span class="op">=</span> <span class="fl">0.5</span> <span class="op">*</span> <span class="fu"><a href="https://rdrr.io/r/graphics/par.html" class="external-link">par</a></span><span class="op">(</span><span class="st">"lwd"</span><span class="op">)</span>,</span>
<span>  polarCircle <span class="op">=</span> <span class="fl">0</span>,</span>
<span>  <span class="va">longitudelim</span>,</span>
<span>  <span class="va">latitudelim</span>,</span>
<span>  debug <span class="op">=</span> <span class="fu"><a href="https://rdrr.io/r/base/options.html" class="external-link">getOption</a></span><span class="op">(</span><span class="st">"oceDebug"</span><span class="op">)</span></span>
<span><span class="op">)</span></span></code></pre></div>
    </div>

    <div class="section level2">
    <h2 id="arguments">Arguments<a class="anchor" aria-label="anchor" href="#arguments"></a></h2>


<dl><dt id="arg-dlongitude">dlongitude<a class="anchor" aria-label="anchor" href="#arg-dlongitude"></a></dt>
<dd><p>increment in longitude, ignored if <code>longitude</code>
is supplied, but otherwise determines the longitude sequence.</p></dd>


<dt id="arg-dlatitude">dlatitude<a class="anchor" aria-label="anchor" href="#arg-dlatitude"></a></dt>
<dd><p>increment in latitude, ignored if <code>latitude</code>
is supplied, but otherwise determines the latitude sequence.</p></dd>


<dt id="arg-longitude">longitude<a class="anchor" aria-label="anchor" href="#arg-longitude"></a></dt>
<dd><p>numeric vector of longitudes, or <code>NULL</code> to prevent drawing
longitude lines.</p></dd>


<dt id="arg-latitude">latitude<a class="anchor" aria-label="anchor" href="#arg-latitude"></a></dt>
<dd><p>numeric vector of latitudes, or <code>NULL</code> to prevent drawing
latitude lines.</p></dd>


<dt id="arg-col">col<a class="anchor" aria-label="anchor" href="#arg-col"></a></dt>
<dd><p>color of lines</p></dd>


<dt id="arg-lty">lty<a class="anchor" aria-label="anchor" href="#arg-lty"></a></dt>
<dd><p>line type</p></dd>


<dt id="arg-lwd">lwd<a class="anchor" aria-label="anchor" href="#arg-lwd"></a></dt>
<dd><p>line width</p></dd>


<dt id="arg-polarcircle">polarCircle<a class="anchor" aria-label="anchor" href="#arg-polarcircle"></a></dt>
<dd><p>a number indicating the number of degrees of latitude
extending from the poles, within which zones are not drawn.</p></dd>


<dt id="arg-longitudelim">longitudelim<a class="anchor" aria-label="anchor" href="#arg-longitudelim"></a></dt>
<dd><p>optional argument specifying suggested longitude limits
for the grid. If this is not supplied, grid lines are drawn for the
whole globe, which can yield excessively slow drawing speeds for
small-region plots. This, and <code>latitudelim</code>, are both set by
<code><a href="mapPlot.html">mapPlot()</a></code> if the arguments of the same name are passed to
that function.</p></dd>


<dt id="arg-latitudelim">latitudelim<a class="anchor" aria-label="anchor" href="#arg-latitudelim"></a></dt>
<dd><p>similar to <code>longitudelim</code>.</p></dd>


<dt id="arg-debug">debug<a class="anchor" aria-label="anchor" href="#arg-debug"></a></dt>
<dd><p>a flag that turns on debugging.  Set to 1 to get a moderate
amount of debugging information, 2 to go two function levels deep, or
3 to go all the way to the core functions. Any value above 3 will be
truncated to 3.</p></dd>

</dl></div>
    <div class="section level2">
    <h2 id="value">Value<a class="anchor" aria-label="anchor" href="#value"></a></h2>
    <p>A <a href="https://rdrr.io/r/base/data.frame.html" class="external-link">data.frame</a>, returned silently, containing
<code>"side"</code>, <code>"value"</code>, <code>"type"</code>, and <code>"at"</code>.
A default call to <code><a href="mapPlot.html">mapPlot()</a></code> ensures agreement of grid and axes by using
this return value in a call to <code><a href="mapAxis.html">mapAxis()</a></code>.</p>
    </div>
    <div class="section level2">
    <h2 id="details">Details<a class="anchor" aria-label="anchor" href="#details"></a></h2>
    <p>This is somewhat analogous to <code><a href="https://rdrr.io/r/graphics/grid.html" class="external-link">grid()</a></code>, except that the first two
arguments of the latter supply the number of lines in the grid,
whereas the present function has increments for the first two
arguments.</p>
    </div>
    <div class="section level2">
    <h2 id="see-also">See also<a class="anchor" aria-label="anchor" href="#see-also"></a></h2>
    <div class="dont-index"><p>A map must first have been created with <code><a href="mapPlot.html">mapPlot()</a></code>.</p>
<p>Other functions related to maps:
<code><a href="formatPosition.html">formatPosition</a>()</code>,
<code><a href="lonlat2map.html">lonlat2map</a>()</code>,
<code><a href="lonlat2utm.html">lonlat2utm</a>()</code>,
<code><a href="map2lonlat.html">map2lonlat</a>()</code>,
<code><a href="mapArrows.html">mapArrows</a>()</code>,
<code><a href="mapAxis.html">mapAxis</a>()</code>,
<code><a href="mapContour.html">mapContour</a>()</code>,
<code><a href="mapCoordinateSystem.html">mapCoordinateSystem</a>()</code>,
<code><a href="mapDirectionField.html">mapDirectionField</a>()</code>,
<code><a href="mapImage.html">mapImage</a>()</code>,
<code><a href="mapLines.html">mapLines</a>()</code>,
<code><a href="mapLocator.html">mapLocator</a>()</code>,
<code><a href="mapLongitudeLatitudeXY.html">mapLongitudeLatitudeXY</a>()</code>,
<code><a href="mapPlot.html">mapPlot</a>()</code>,
<code><a href="mapPoints.html">mapPoints</a>()</code>,
<code><a href="mapPolygon.html">mapPolygon</a>()</code>,
<code><a href="mapScalebar.html">mapScalebar</a>()</code>,
<code><a href="mapText.html">mapText</a>()</code>,
<code><a href="mapTissot.html">mapTissot</a>()</code>,
<code><a href="oceCRS.html">oceCRS</a>()</code>,
<code><a href="oceProject.html">oceProject</a>()</code>,
<code><a href="shiftLongitude.html">shiftLongitude</a>()</code>,
<code><a href="usrLonLat.html">usrLonLat</a>()</code>,
<code><a href="utm2lonlat.html">utm2lonlat</a>()</code></p></div>
    </div>
    <div class="section level2">
    <h2 id="author">Author<a class="anchor" aria-label="anchor" href="#author"></a></h2>
    <p>Dan Kelley</p>
    </div>

    <div class="section level2">
    <h2 id="ref-examples">Examples<a class="anchor" aria-label="anchor" href="#ref-examples"></a></h2>
    <div class="sourceCode"><pre class="sourceCode r"><code><span class="r-in"><span><span class="co"># \donttest{</span></span></span>
<span class="r-in"><span><span class="kw">if</span> <span class="op">(</span><span class="fu">utils</span><span class="fu">::</span><span class="fu"><a href="https://rdrr.io/r/utils/packageDescription.html" class="external-link">packageVersion</a></span><span class="op">(</span><span class="st">"sf"</span><span class="op">)</span> <span class="op">!=</span> <span class="st">"0.9.8"</span><span class="op">)</span> <span class="op">{</span></span></span>
<span class="r-in"><span>    <span class="co"># sf version 0.9-8 has a problem with this projection</span></span></span>
<span class="r-in"><span>    <span class="kw"><a href="https://rdrr.io/r/base/library.html" class="external-link">library</a></span><span class="op">(</span><span class="va"><a href="https://dankelley.github.io/oce/">oce</a></span><span class="op">)</span></span></span>
<span class="r-in"><span>    <span class="fu"><a href="https://rdrr.io/r/utils/data.html" class="external-link">data</a></span><span class="op">(</span><span class="va">coastlineWorld</span><span class="op">)</span></span></span>
<span class="r-in"><span>    <span class="fu"><a href="https://rdrr.io/r/graphics/par.html" class="external-link">par</a></span><span class="op">(</span>mar <span class="op">=</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html" class="external-link">c</a></span><span class="op">(</span><span class="fl">2</span>, <span class="fl">2</span>, <span class="fl">1</span>, <span class="fl">1</span><span class="op">)</span><span class="op">)</span></span></span>
<span class="r-in"><span>    <span class="co"># In mapPlot() call, note axes and grid args, to</span></span></span>
<span class="r-in"><span>    <span class="co"># prevent over-plotting of defaults.</span></span></span>
<span class="r-in"><span>    <span class="fu"><a href="mapPlot.html">mapPlot</a></span><span class="op">(</span><span class="va">coastlineWorld</span>,</span></span>
<span class="r-in"><span>        type <span class="op">=</span> <span class="st">"l"</span>, projection <span class="op">=</span> <span class="st">"+proj=ortho"</span>,</span></span>
<span class="r-in"><span>        axes <span class="op">=</span> <span class="cn">FALSE</span>, grid <span class="op">=</span> <span class="cn">FALSE</span></span></span>
<span class="r-in"><span>    <span class="op">)</span></span></span>
<span class="r-in"><span>    <span class="fu">mapGrid</span><span class="op">(</span><span class="fl">15</span>, <span class="fl">15</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="op">}</span></span></span>
<span class="r-plt img"><img src="mapGrid-1.png" alt="" width="700" height="700"></span>
<span class="r-in"><span><span class="co"># }</span></span></span>
<span class="r-in"><span></span></span>
</code></pre></div>
    </div>
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