Reading 4 and 6 figure Grid References.
As UK Scouts, we make use of the Ordnance Survey Maps as a standard for navigation. So that we can get from one place to another, we use 6-figure “Grid References” to accurately identify the various points that we are talking about. Using these references, we can create a route going from point to point (if you have a GPS device, these are often referred to as “waymarkers”).
On an Ordnance Survey map is a grid of Blue Lines going vertically and horizontally (there are squiggly blue lines as well, but they’re rivers and waterways 
) Each of the blue lines usually has a number somewhere along its length. The following is a map of Lees Wood Campsite:
(Above: Lees wood map by Ordnance Survey. See end of blog for further acknowledgements)
Below is a simple grid diagram, with numbers along the top and the side. In one square I have an eye – and I want to give you the grid reference for that. Because it is such a big thing in the grid, I can give you a four figure grid reference – 03 83.
There are many ways to help you remember the order of the numbers; the way I remember is drawing the letter “L” as you always go down first, then across. Also, the zero in “03” is also important – if you miss giving it someone could read the reference as 38 3 – a wholly different place.
A quick exercise – what’s the 4-figure grid reference that has the two circles?
So that brings us onto the next challenge – when there’s only one thing in the square, four figures fine. But that puts it into a 1km square area – not very accurate. A 6-figure reference gives us a better accuracy – a 10m square area.
6-figure reference isn’t much harder to do. Let’s give a 6-figure grid for the Grey circle. We know that the 4-figure grid is …. 02 82 (did you get that?). What we do is divide that square up with ten more vertical and horizontal lines – effectively giving us a “decimal point”. Just using a rough estimate, the grey circle can be calculated as :
02 grid line, plus it’s about 0.8 of the way across to the next grid line – 028
82 gridline, plus it’s about 0.3 of the way up to the next line – 823
So the 6-figure grid reference for the grey square is 028 823.
Soo… what’s the 6-figure grid reference for the square?
Other things to note:
- If the object crosses the grid line, then the 6-figure grid reference will be a zero.
- You may see a couple of letters in front of the grid reference – this defines a certain area and is especially important to start to pin point down the area that the grid reference refers to (in most hikes, this isn’t really needed as the map usually isn’t that big an area)
- You can record 8-figure grid references; this is accurate to 1m square – and is mostly used by the military (and by GPS units… although many are never that accurate to start with!)
VERY IMPORTANT THANKS:
Lees Wood Map Reproduced from Ordnance Survey map data by permission of Ordnance Survey, © Crown copyright.
Image produced from the Ordnance Survey Get-a-map service. Image reproduced with kind permission of Ordnance Survey and Ordnance Survey of Northern Ireland.
Copies of Get-a-map mapping for teaching and classroom use:
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