General
Ireland is covered by a square grid measuring 500km to a side. This is
sub divided into 25 100km square areas, each one of which is given a
letter. The letters used are A, B, C, D, E, F,
G, H, J, K, L, M, N, O,
P, Q, R, S, T, U, V, W, X,
Y, Z - the letters in bold being the ones that contain land mass.
Each side of these 100 km squares is further divided into 1000 units, each one
representing 100m. Using these the position of a place can be given as a grid
reference, which will look something like N 387 234. This first of all
means that the place you are looking for is located in square N. You then
use the other two numbers to locate the place you are looking for.
To use the number parts of our grid reference let's take the first part, which is called
the 'easting'. Across the bottom of an OS map you will see numbers that are
between 00 and 99. These represent 1km i.e. 10 of our 100m units. So to locate 387
we find the vertical line numbered 38, we will come to the 7 in a moment. Then
we take the 23 part of the 'northing' value (234) and find the horizontal
line numbered 23 up the side of the map. Once you have these two lines find the point where they cross. This is
actually the point N 380 240. Now we have to deal with the 7 and the 4.
To do this you have to divide each side of the square you have just located into 10 smaller units.
Then we just go across from our point of intersection 7 of these units and up 4.
A useful thing to remember at this stage is that on a 1:50,000 scale map one of these smaller
units measures 2mm.
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