Grid References

Grid References


The ability to quote quote accurate Grid References from a map is a key skill to gain early in your hill walking career


Grid References 

Calculating Grid References



A key skill to learn as early as possible in your walking career is to be able to calculate an accurate Grid Reference from a map. You will need grid references when planning a walk (if you follow best practice) and in cases where you need to call for help, your location is the important piece of information the emergency services need from you.  A grid reference is a universal language to describe your position on the ground within Great Britain. 

Calculating an accurate grid reference takes practice if you are to become proficient at doing it on a hill, in bad weather etc. The principles are simple, but it can be confusing sometimes when learning. Practice in the comfort of your lounge!


British National Grid Re-cap

(If you've not read the section about the British National Grid, click here.)

You already know how the British National Grid is constructed, so that’s a good start. A re-cap from the previous section

  • The grid is made up of 25 500km by 500km squares, each of which has a letter. Only squares S, T, N & H fall over the land mass of Great Britain

  • The 500km by 500km squares are further sub-divided into 25 more squares, each being 100km by 100km, and allocated a letter of the alphabet (the letter 'I' is excluded)

  • The combination of the above two letters uniquely identify an area of 100km square, for example SD, which covers north west England

  • When quoting a grid reference you must also prefix the numers with the two character alphas so that you uniquely identify the correct 100km by 100km larger grid square


Northern Ireland

This site is aimed at the UK hill walker. However, at this time it does not give information about the different grid system used in Northern Ireland. Please be aware that information quoted relates to England, Scotland & Wales only, i.e. Great Britain & the British National Grid.


The Grid Reference

A grid reference is used to identify a geographical location by using the grid squares from the British National Grid. To describe a single 1km by 1km grid square within Great Britain, you could quote a 4 digit grid reference, and this is a good place to start to learn the process. However, you will soon realise that 1km square is quite large, and 4 digit references are not precise enough for use in the hills. This is why it's normal to quote what's called a 6 digit grid reference, which identifies an area 100m by 100m, which might sounds a lot, but it's about as accurate as you can be with a 1:50,000 map (as 100m is represented by 2mm on the map).

In theory you can calculate an 8 digit grid reference, which identifies a 10m by 10m square, and even a 10 digit reference, which is 1m by 1m. Some GPS units quote to that level of detail, but 10 digits is overkill for most uses, and 8 digits is pushing it. 6 digit grid references are the most common, and commonly understood by people.


What Does a Grid Reference Look Like?
A 6 digit grid reference written properly is always in the following format:

  • two letters, followed by

  • two sets of three numbers

  • the first set of three describe the eastings (horizontal)

  • the second set of three numbers describes the northings (vertical)

  • for example, SS 858 416


Video

This video is produced by Ordnance Survey and is a good introduction to grid references.





Key Points

  • Always quote the Eastings first (the ‘x’ axis, or 'along the corridor')

  • The second set of digits are the Northings (the ‘y’ axis, or 'up the stairs')

  • Sub-divisions of the 1km grid squares are made by estimation, or by using what’s called a ‘roamer scale’, which is found on some compasses or as a separate piece of kit

  • Divide the 1km square into a 10 by 10 grid


Map Case Tip

When you fold your map and put it in a case, make sure that you can see numbers associated with grid lines. If you can't, write a few onto the map before folding, so that you don't have to risk getting your map out of the case when on the hill in the situation of your needing to use a grid reference.


Demonstration

Take a look at the following pages for a step by step guide to grid references (press 'next'), or press 'previous' to go back.