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The location of a postcode is defined as the average of the location of all the addresses in that postcode.

The location returned from this service is accurate to within 100 metres of this average location.

The location of a town, street or other free-format address elements is defined as the average of locations of all the postcodes in that area, weighted by the number of addresses that use that postcode. This may differ slightly from the locally-known "heart" of the area.

Missing Locations

Locations are not available for certain postcodes, including:

Longitude and Latitude

The locations provided by Ordnance Survey are produced according to the OSGB36 datum. GPS based systems and many other worldwide systems such as online mapping tools use the WGS-84 datum. You can choose which datum to use for the longitudes and latitudes returned by this service. By default, the WGS-84 datum is used.

To select your preferred datum, you can supply an Option to the FindLocation or Geocode methods with a name of Datum and a value of either OSGB36 or WGS84 as appropriate.

As the original data is provided according to the OSGB36 datum, it is more accurate when using that datum. When converting the data to the WGS-84 datum, the accuracy can be reduced.