text: Postcode area names Postcode areas are usually, but not always, named after a major town or city – such as B for Birmingham. Some are named after a smaller town (e.g. Southall postcode area is UB after Uxbridge) or a combination of towns (e.g. SM appears to be named after Sutton and Morden). A small number are geographic in nature – such as HS for the Outer Hebrides, FY for Fylde (the region around Blackpool) and ME for the Medway conurbation, with Rochester as its main post town.  In the case of London (a Post Town), there is not a single "London" postcode area; rather there are eight (N, E, EC, SE, SW, W, WC and NW) reflecting the preceding system for coding London based on compass points. In the case of Northern Ireland, the entire province has a single postcode area BT (named for Belfast). Postcodes generally do not align with historical county or local authority boundaries, and can also cross national boundaries (e.g. CH and TD postcode areas).
  Postcode districts and numbering
  The initial system of named postal districts, developed in London and other large cities from 1857, evolved towards the present form: in 1917 London was split into broad numbered subdivisions, and this extended to the other cities in 1934.
  Each postcode area contains a number of post towns and postcode districts.  Example: a sizeable part of southern England is covered by the GU postcode area, named after the town of Guildford. Guildford itself consists of postal districts GU1 and GU2. Nearby Woking, a major commuter town—10 km away—is a post town within the postcode district GU22.