Grid references can be practiced anywhere. Here practicing navigation in the Peak District on a snowy day with a small country lane running to the distance along a fence, framed by snow covered fields.
Navigation Lessons

Compass Corner: Lesson 2 – Why are Grid References so Important?

I have decided to cover this important skill early into the series, as it is so crucial in an emergency situation. Knowing how to find out the grid reference of your location, either using a map or another tool, can make all the difference when things go wrong. It is especially important to know how grid references work, if you ever need to alert the Mountain Rescue, or another rescue service. The brilliant thing about grid references is that they will always accurately describe your location anywhere in the UK. Recently other services, such as the What3Words, have become popularised for the same purpose. However, there are reasons why these might fail you on the hills and mountains, which I will discuss below.

What are grid references?

Grid references describe specific locations on a map, any map, based on a set of numbers called eastings and northings. The horizontal and vertical lines forming squares on maps are a part of an indicate coordinate system, based on which it is possible to describe any location on the map. When using an international grid system, such as the Universal Transverse Mercator (UTM), any location in the world can be described using a grid reference for it. The system is universal and, therefore, it does not matter if people use maps of different scale or type. However, in the UK the most commonly used grid system is the Ordnance Survey National Grid (also known as the British National Grid).

Ordnance Survey National Grid divides Britain into 100km x 100km squares, each identified by two letters. These letters are unique to the area and always the same, no matter which map scale you are using. In case you missed the last lesson where we discussed map scales, have a look here!

How to take a grid reference using a map?

Many people are needlessly intimidated by the prospect of using grid references. Maybe it is the use of numbers, or the associated jargon which puts people off. But to be honest, taking a grid reference is very simple if you know where you are. And even if you only have a vague idea – you will be able to give a less precise location using the same system. Which is part of why it is so brilliant!

Aim for a six-figure grid references

So, every OS map has a set of two numbers on it (sometimes there are more that one set). These are printed on blue on the map and can also be found by having a look at the map key. These two letters indicate the 100km x 100km square of Great Britain you are in. The first one of these letters will usually be S, T, N or H.

By adding a set of 4-10 numbers behind these letters you will be able to give increasingly accurate descriptions of your location. These numbers constitute the eastings (increasing eastwards on the map) and northings (increasing northwards on the map). A four-figure grid reference indicates a 1km x 1km square on the map. You might remember from the last lesson that this is the usual size of a square indicated by blue lines on the map.

In order to give more precise locations than this, you will need to divide the visible squares into smaller parts. A six-figure grid reference is formed by dividing the visible square in to 10 equal parts both horizontally and vertically. This means that a six-figure grid reference gives you a location with the accuracy of 100m x 100m. It is possible to give even more precise locations with eight-figure grid reference indicating a 10m x 10m square. And ten-figure grid reference indicating a 1m x 1m square. However, these are rarely used, impractical in the wild and – to be honest – rarely necessary.

Steps to find a grid reference:

  1. Find the two letters indicating which 100km x 100km square of Great Britain you are in.
  2. Find the two numbers at the bottom (or top) of your map denoting eastings. Then find the two numbers at the left-hand or right-hand edge of your map denoting the northings.
  3. Locate which square of the map you are in. List the numbers with the easting first and the northings after. A memory rule I use for this is ‘go along the corridor and up the stairs’. Meaning first go along the map (from left to right) and then up the map.
  4. Once you have located the right square, imagine this is divided into further 10 pieces both horizontally and vertically. Repeat the earlier process and add the precise location by adding a third digit to the eastings and northings.
  5. Well done! This is your six-figure grid reference, which will accurately describe your location anywhere in Great Britain. (While this process is illustrated using the OS Grid System specific for Great Britain, grid systems and coordinates function on the same principles anywhere in the world!)

Example using an OS map:

Let’s look at this randomly chosen OS map a little closer. The letters for this area are SE, which can be found clearly indicated on the map with blue capital letters. The eastings visible on this part of the map are 00, 01, 02, 03 and so forth. Whereas the northings are 16, 17, 18, 19 and 20.

Four-figure grid reference:

So, every blue square on this map is 1km x 1km and, therefore, can be indicated with a four-figure grid reference. So, let’s find the grid reference for the square which includes Pike End (denoted with a red arrow). We start with the letters SE, followed by the easting 02 and the northing 17. This makes the grid reference SE 0217. To remember the order of the numbers I use the saying ‘along the corridor and up the stairs’. Although many others exist too! The important thing to remember here is to always read the numbers in an increasing order. The easting for this location is 02 (NOT 03) because we read from left to right in an increasing order. Similarly, the northing for this square is 17 (NOT 18) because we read from bottom to top in an increasing order.

Six-figure grid reference:

Now to find the ever important six-figure grid reference. For that we need to have a more precise location in mind. Let’s use the building at the end of the footpath, indicated with a blue arrow. In order to find that we need to divide this square into 10 even parts horizontally and vertically. Personally, I do this by imagining a middle line in both directions (red lines below). If we want to find out the easting for the building, we count how many parts along the location is from left to right. In this case it is right by the second green line. We repeat this from bottom to top and can clearly see that the location is on the centre line, which is the fifth part.

This gives us the final grid reference. Reading left to right (along the corridor) and bottom to top (up the stairs) the whole six-figure grid reference becomes:

SE 022 175

Letters SE, easting 02 plus 2 parts along, northing 17 plus 5 parts up.

Well done, you now know how to take grid references using a map! This same process can be done using any map and with a little practice becomes so quick that you can estimate the location with just a glance! And to be honest, if you need to give your location to a rescue team in an emergency, and make a small mistake, they will still get very close to you despite the little inaccuracy!

Can I use a phone or a GPS device to find out grid references?

Most handheld GPS devices and watches will be able to give your grid reference to a great degree of accuracy. With phones this is a bit more complicated. Technically, the OS Locate app is an excellent tool and will give you an accurate grid reference for your location. In reality, however, every app is only ever as accurate as the GPS in your phone. And that varies greatly. OS explains on their website that:

‘The location shown relies on information from the hardware in the phone/tablet. GPS works best with a clear view of the sky. The accuracy will depend on your device and local conditions, and will generally improve if you remain still for a few moments. We only show six-figure grid references as this is accurate as most phone GPS chips will support. GPS location is normally around 15m accuracy in good conditions.

Most smartphones, when unable to get an accurate GPS location will show the best guess. This may often be the location of the nearest mobile phone tower, so could be several kilometres away. The location shown will sometimes jump around as your device calculates a more accurate position.’

Why you should never rely on What3Words in remote areas?

Now I know this is going to be a controversial bit of this article – but hear me out. The What3Words app has recently been popularised among walkers and emergency services alike. This is largely due to the impressive advertising campaigns put out by the highly efficient promotional team behind What3Words. However, there are a few worries which repeatedly arise when talking to people involved with Mountain Rescue in remote areas.

Points of Contention:

Firstly, What3Words like any other app on your phone relies on the accuracy of your phone’s GPS. Which to be honest isn’t always great (see the above discussion on OS Locate). Therefore, while it might be a great tool in certain areas, its reliability declines drastically, not only if your phone has a poor GPS, but also in rural areas and bad conditions.

Secondly, What3Words is a private company and it is not open source. This means that the grid system they use is not available to publicly view (unlike the OS grid which is available for everyone). It also means that all requests for a location using their words needs to go through their servers. This on its own makes the system risky, as it is only viable as long as this company is trading, and its servers are up. Which brings us up to the next issue. As a private company the What3Words does not currently charge charities, such as mountain rescue, or emergency services for its use. However, there are no guarantees that they will not become a paid-only service in the future. This, understandably, causes some discomfort among the mountain rescue, and other charities, which are relying on donations to function.

Thirdly, words are difficult. Random unconnected words are even more difficult. Therefore, without extensive use of the phonetic alphabet (which not everyone knows) the risk of getting the words wrong over the phone is rather large. More so if background noise (such as high wind) is involved. And if a text message is used to convey the location… Well there already exists a number of rescue specific ways to locate your phone. (Such as SARLOC, which is designed for this purpose and regularly used by the rescue services.)

Further Discussion:

In the tech circles people much more qualified than me have for a long time discussed some of the issues with What3Words. Most of these discussions end up pointing back to a 2013 blog post titled Why Bother with What Three Words. I am not qualified to discuss the claims made in this blog put wanted to bring it to your attention in case the topic interests you.


The What3Words can be a great tool, especially in populated areas, but should not be relied upon as your only way of providing you location. However, the importance of a system like it is highlighted when help is needed in areas of the world where addresses are rarely used. It is also great that more resources are dedicated to making outdoor activities safer. Yet it should be noted that What3Words, as a profit-oriented company, might not be around as a permanent service. Therefore, to depend on it too much might lead to problems later if the service becomes unavailable for any reason.

So, it is crucially important to know how to use a map to give your OS grid reference. It is a stable and reliable way which all rescue services are able to use regardless of other available services. (In fact, if you send a What3Words location to a mountain rescue team – the chances are they will convert it to a grid reference anyway!) In addition, I recommend everyone to register for the text 999 service to make getting in touch with the emergency services as easy as possible!

Other articles you might be interested in:

The Compass Corner Navigation Lessons Syllabus

Compass Corner: Lesson 1 – How to Read a Map

Clothes for Cold: How to Layer for Autumn & Winter Walking

How to Start Hiking: A Guide to Hiking for Beginners

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