Ordnance Survey maps are covered in a series of faint blue lines that makeup a grid. The lines have numbers accompanying them that allow you to accurately pinpoint your location on a map. Once you have located where you are, the grid system makes it simple to give others (such as mountain rescue) an accurate description of your location. This description, which will be a series of numbers, is known as a grid reference.
Download the OS handout on the National Grid
There are two main types of grid reference:
4-figure – for example, 1945, this indicates a single kilometre square on an Ordnance Survey map.
6-figure – for example, 192454, shows a point within a 100m square.
4-figure map references
When giving a 4-figure grid reference you should always give the eastings number first and the northings number second, very much like when giving the reading of a graph in school – you must go along the corridor/hallway (horizontal) and then up the stairs (vertical).
6-figure map references
Having worked out the basic 4-figure grid reference imagine this square is further divided up into tenths.