why are there squares on maps?

Maps come in varying sizes, usually too large and doing its best to rip itself from your hands on a windy day, and they come in varying scales, usually giving seemingly insufficient detail or confusingly too much.

Nevertheless what all maps have in common is a printed overlay of squares, the 'grid', each containing the detail being mapped for one square kilometre on a typical hiking map.


Here, Chris Townsend from the British Mountaineering Council will take you through the practicalities of establishing a 'grid reference' from a map should you need to work out or share an exact location.



Maps have been in use in the UK for political, military, or other uses for centuries and they became quite the fashionable thing in Victorian times, with all kinds of public agencies and private individuals producing their own to various levels of detail and scales. The 1-inch to 3-inch chains scale being one of the most widely used*.

It was as late as 1919 when a seminal thought occurred 'a National Grid should be superimposed on all large scale plans and on smaller scale maps, to provide one reference system for the maps of the whole country' and the first practical steps were taken by the Ordnance Survey to provide one version of the truth for the whole of Great Britain and its territorial waters. The current 'British Grid' (BG) was the result.


Using the Squares

At their largest the BG grid squares have sides representing 500km and each is assigned a letter running from A to Z, but missing out the letter I. This has the twin benefits of avoiding potential confusion with the number 1 and of neatly making 25 grid squares in a 5 x 5 layout. A genius move making things very much the easier to deal with, imagine the faff of having 26 squares in this and the subsequent sub-division.

Each 500km grid square is sub-divided into smaller squares with sides 100km that are themselves each given a letter for identification and used sequentially together with the 500km letter to define an area.

Not all of the 100km squares are of practical use for 'topography' (a map of physical features of an area) because there is nothing there but sea.

Take a look at grid squares NE and TB on the diagram, nothing but sea to see there. OK so there might be a small island in there somewhere but it is hardly going to be big seller for the Ordnance Survey to produce a map for it, so they don't. The Admiralty's charts department does however, should you be so inclined toward messing around in boats.

So far so good should you wish to know where Cornwall sits in the British Grid (Grid Reference: SW), but further detail is required for practical use by mountaineers.


Zooming In