Updated March 2020.
On week four in our six-week blog series on map reading skills, we’re taking a look at how to read a grid reference. Map reading is an essential skill for any explorer or outdoor enthusiast. We’ve teamed up with Steve Backshall to record a series of videos to remind you of the basics and help you feel confident with your map.
So far we’ve covered which OS map you need, understanding map symbols and making sense of contour lines. Today we’re covering grid references, both four-figure and six-figure version. Over the next fortnight we’ll also cover:
- Knowing your compass and how to take a compass bearing
- Understanding magnetic north
Each week we’ll share Steve’s video with you, give a summary in the blog and point you in the right direction of further resources and details. Hear what Steve has to say about grid references in these two short videos:
Why do we need to know how to read a grid reference?
As Steve said, it really could save a life. Our and about in urban Britain, if you spot an accident and call the emergency services, chances are that you’ll be able to give an address, street name, postcode etc. But if you’re out walking and you fall and injure yourself – it is unlikely that you will know the postcode of where you have fallen. If you’re able to provide six figure grid reference of where you are that narrows your location down to a 100 metre square box and could make a huge difference to how quickly the emergency services can get to you.
How to read a four-figure grid reference
Whether you are using an OS Explorer Map (the orange ones) or an OS Landranger Map (the pink ones) you’ll notice that the map is covered with a grid of thin blue lines that form square boxes all over the map.
Each line, whether running vertically or horizontally across the map has a number on it (both at either end of the line and somewhere halfway along).
The numbers that run from left to right (or west to east) on the map are called Eastings – this is because the number of the line increases the further east you go.
The numbers that run from bottom to top (or south to north) on the map are called Northings – this is because the number of the line increases the further north you go.
Using OL13 for the Brecon Beacons as an example, imagine we are following the Three Castle Walk near its crossing with Bont Brook and want to let people know where we are. To take a four figure grid reference you take the Easting first (taking the number that is bottom left of the square you are looking for) and then the Northing. Regardless of which map you are using – this places you in a 1 km square box, in this case, 3920.
Great Britain is also broken down into 100 km square boxes – each has a prefix of two letters. These letters can be found in each of the four corners of your map. Add these to the start of your grid reference and you have pin pointed your exact location. In this case, we’re in square SO, so our four figure reference is SO3920.
How to read a six-figure grid reference
If you want someone like the emergency services or mountain rescue to come to you quickly – you’ll want to narrow down the area by creating a six figure grid reference – this will then place you in a 100 metre box.
What you need to do is imagine that that one box identified in your four figure grid reference is broken down into smaller squares – 10 x 10 squares, which are marked all around the edges of your map.
Starting with “0” as the number of the first box – count across from the Easting line to where you are and add this to your Easting number of your four figure grid reference.
Then you do the same with the Northing – starting with “0” in the first box – count up how many squares you are from the bottom northing line of the square.
Putting these together you have your six figure grid reference so this puts us at SO393203.
You can download our resources from our Map Zone (aimed at children) that take you through how to take a grid reference with more examples. So that’s it – my lesson on how to take a grid reference is over. Now you can take to the hills and be able to tell someone where you are!
Happy exploring! I’ll be back next week to talk about how to use a compass.