The National Grid

In order to reference any point in mainland Britain (England, Scotland and Wales) the area has been divided into a grid of 100km squares. Each square has then been given a unique two letter code (see right).

Each 100km x 100km square is then further subdivided into 1km x 1km lines which are overprinted on Ordnance Survey maps.

By further subdividing this 1km x 1km grid it is possible to give coordinates to any 100m x 100m square anywhere in the country using a 6 figure reference number.

Since this 6 figure reference number can be duplicated in each of the 100km x 100km squares, you must add the two letter grid identifier to make the grid reference truly unique.

For more details see Giving a Grid Reference.