Grid ref numbers

These 100km squares are then subdivided into ten 10km squares, starting from the southwest corner and numbered 0-9 horizontally and vertically. These are again subdivided into ten 1km squares numbered 0-9.

As the 1km squares are the most frequently marked on the map (and, generally, the ones you most need to use), what this looks like in reality is a grid of 1km squares numbered 00-99 both horizontally and vertically.

So for example, SH6054 (area reference SH and 1km grid square reference 60 horizontally and 54 vertically) is the four-figure grid reference for Snowdon summit and gets you to the 1km square containing the top of Wales’ highest peak. The horizontal numbers (eastings) always come before the vertical numbers (northings) – think ‘along the corridor then up the stairs’.

To get more precise than that, you need to get your compass out and start measuring. You can get as precise as a 1m x 1m square grid reference, but for most of us a six-figure grid reference (which gives a 100m x 100m square) is sufficient for all but the most detailed navigational needs.

4 digits = 1km x 1km square

6 digits = 100m x 100m square 8 digits = 10m x 10m square 10 digits = 1m x 1m square

Eastings are the vertical lines which increase in value as you read east (left to right) across the map. Northings are the horizontal lines which increase in value as you read north, up the map from bottom to top. Eastings always come before northings in grid references, so measure across and then up.

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