What are they?

To make it easier to read a map, it is split into squares more commonly known as a grid.

The lines of the grid a numbered so you can make a reference to them. This means that you can say the hospital is in square X and someone else can immediately go to that square to find it rather searching the whole map.

On an Ordnance Survey Explorer map, which has a 1:25,000 scale, the size of the squares is 4cm x 4cm. This means that each square is a square kilometre on the ground. With the squares representing this easy to remember distance, you can get a rough idea of how far two points are apart just by looking and not having to go through the process of taking a measurement.

Grid Referencing

When you make a reference, you can give it in 4 figures. 2 figures for the vertical and 2 figures for the horizontal. This can be read directly off the gridlines on the map. An example of a 4 figure grid reference would be (13,05). This refers to the square that is to the right of line 13 and above line 05.

Remember that the first number always denotes whereabouts in the West-East direction, and the second is in the North-South direction. An easy way to remember this is 'along the corridor and up the stairs', where the first number tells you how far along the corridor it is, then the second number is how far up the stairs.

This type of referencing is often unsuitable though as it refers to a whole square on a map. As the squares are 1km x 1km in size, it is a lot of area to cover if you are out in the wilderness looking for a certain rock or in a town looking for a telephone box.

6-Figure Referencing

To get around the above problem of a large area to a grid reference, we take a square and divide it up into imaginary smaller squares forming a small 10 x 10 grid. Each of these is numbered from 0 to 9. This means that you can narrow down a grid reference to a square 100m x 100m in size. This is a lot more useful as it means you have a much smaller area to look in.

Referencing one of these smaller squares is done in 6 figures. This time 3 figures for vertical and 3 for horizontal. An example of this would be (134,057). This still means that it is in the big square (13,05), but the third numbers denote which of the smaller squares it is in. In this case it is in (4,7) of the small grid in the big square (13,05).

This can be quite hard to get to grips with at first. One of the easiest ways to think about it is as a ruler. If you imagine the big squares are centimetres, then the small ones are millimetres. When you give a grid reference though, you do not include a decimal point!

This process can be repeated to give an 8 figure grid reference and hence a 10m square, but this is very difficult as it gives squares on a map that are only 0.4mm in size, which is very difficult to measure!

As you probably won’t have a ruler to hand when you are out map-reading, your compass often has a scale written on it that can be used to find grid locations. This is called the ‘Romer Scale’ and is very handy! Check that the scale on your compass is the same as the scale shown on our map.