Knowing how to read a Grid reference is fundamental to be able to navigate effectively. In this section, we are going to explain what they are and how to read grid references to show your location. We will be basing this section on the British Grid system created by Ordnance Survey but once you grasp the concept of one grid system they will all come naturally with a little practice.

A grid reference defines a specific square area on the ground. How small the area is and therefore how accurate the grid reference is, depends on the detail of the grid reference. So let’s start with first working out what part of the grid we are in. To narrow down our area from the whole of the UK to 100km².

In the map above you will see that the UK has been divided up into squares of 100km by 100km. Inside each of the grids is a map with 1km squares numbered from 0 to 99 east and north, because all the maps have the same numbers(0-99) than if you provided a grid reference of say 1984 then you could be at that point in any of the 52 active areas in the national grid. The two letters that represent each area of the UK you are in are a way of avoiding this error by differentiating each grid area. In the bottom corner of the map, you will see two letters which àre the area you are in. Make sure you know what it is so that if you had to tell someone where you were then you could start with those two letters for instance SH if you were somewhere in Snowdonia(north Wales).

So with those two letters we have narrowed ourselves down to an area of 100km², we now need to narrow ourselves down a smaller area. Each grid is divided into 100 boxes that are used to narrow your position down to 1km². Those 1km squares are what the grid lines on a map show so whether you are on a 1:50000 scale map or a 1:25000 scale map you will have grid lines covering an area 1km wide and 1km tall because all metric grid systems are the same.

The way a grid system works is that you work out which box you are in, and then use the numbers on the easting and northings(grid lines), to give yourself a grid reference of the box you are in. Take the example below, we have an area of map within one of the national grid squares which in this case is ‘TM’.

A grid reference starts on the bottom left corner of the box, so first we need to take the number of the grid line that lines up with the left-hand side of the box we are in. So for the Green square marked on the map that would be 12 as that line is to the left of the green box. Next, we need to use the northings to get which row we are in so again for the green square it would be 32 because the bottom of the green box lines up with that line. Now that we have our easting and northing we can put them together to make a 4 figure grid reference which in this case is TM 1232.

The Easting always goes before Northing. An easy way to remember this is ‘Along the corridor and up the stairs’, so you first go across the map and write down that number and then go up the map and add that number, be sure to make sure these are the right way round else you will be pointing to an entirely different place.

Now lets do another example with the Black box. The left-hand side of the box is on line 18, the bottom of the box is on line 35. We are still in the same area so the GR is TM 1835.

Have a go yourself and try and work out the grid references for the three orange boxes.

So we have made a 4 figure grid reference that puts us in a 1km² area which is good but not really accurate enough for most situations out in the field so we are now going to learn about how to make it more accurate with a 6 figure grid reference which gives us an accuracy of 100m². To work out a 6 figure grid reference you take the grid that you are in and pretend that grid is divided into 10×10 squares like the diagram below.

From the zoomed out image we can work out the 4 figure grid reference is TM 19 36. We can then divide the square into 10 boxes to add the two other numbers that make the 6 figure grid reference. It works in exactly the same way as working out a 4 figure grid reference in the fact that you first go along the bottom and find the line that covers the left-hand side of the box you are in, then you go up the square to find the line that covers the bottom of the square you are in.

Let’s take the ‘B’ from Bylam farm as a location, first, we go along the bottom and find the line that covers the left-hand side of the box that the ‘B’ is in which is 4. We add that to our eastings from the 4 figure grid reference and we have TM 194. Then we work out our northings so we go up and find the line that covers the bottom edge of the box that the ‘B’ is in which is 8. We add that to the Northings we worked out making TM 36 into TM 368. Put that all together and we have TM 194 368 which is our location to an area of 100m².

On the map there won’t be any lines to work out the 6 figure grid reference, you can either try and judge it by eye or you can use what’s called a roamer which is a see through piece of plastic that you can put over the section of map to be able to accurately separate the grid into 10 boxes. They will be found on any good compass or can be bought separately.

Have a go yourself and try to find the grid reference of both the ‘S’ in Spring and the number 25 on the contour line.

Need to be more accurate? You can use 8 figure grid references which give us an accuracy of 10m², they work in the exact same way a 6 figure grid reference does, you just divide the square of your 6 figure grid reference into 10 more squares and add the number for the easting and northing. The bottom of the line in TM 191 362 would have 8 figure grid reference of TM 1918 3624.

You should now have a good understanding of how grid references work and how to give a grid reference from your location or work out a location from a grid reference. If you are unsure of anything then take another read through before you move on, or ask us in the comments.

Next, we are going to talk about planning your route and deciding where to go.

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