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1. The large rectangles on the map lettered A, B, C, etc., are divided into squares, loooyd. side, which are numbered I, 2, 3, etc. Each of these squares is subdivided into 4 minor squares of 500 vd. side. These minor squares are considered as letters a, b, c, d (see square No. 6 in each rectangle). A point may be thus described as lying within square B.6, M-5, b, etc.

2. To locate a point within a small square, consider the sides divided into tenths and define the point by taking so many tenths from VV. to E. along southern side, and so many from S. to N. along western side, the S.W. corner always being taken as the origin, and the distance along the southern side being always given by the first figure. Thus the point Z would be 63 ; i.e. 6 divisions east and 3 divisions north from origin.

3. When more accurate definition is wanted (on the 1 :2O,ooo or 1 : 10,000 scale) use exactly the same method, but divide sides into 100 parts and use four figures instead of two. Thus 0847 denotes 08 parts east and 47 parts north of origin (see point X). Point Y is 6503.

4. Use o but not 10; use either two or four figures; do not use fractions (8j, 4!, etc.).

DIAGRAM

x

Z

&

The system of reference by squares shown on the map and described above was used through- out the war by the British armies on the western front. Although clear and simple in practice it was not ideal for gunnery purposes. For this reason it was decided shortly before the Armistice to supersede it by another and more universally useful system (see article SURVEYING: Military).

CONVENTIONAL COLOURS AND SIGNS

Colours. The topography was represented in three colours. The detail including towns, houses, railways, roads, woods and grid lines and numbers, was printed in grey, water in blue, and contours in brown.

Military details such as trenches, battery positions, mine craters, obstacles, etc., were shown in blue (British) and red (German). British trenches were not shown in extenso, but only for such distance from the front line as might be assumed to be already well surveyed by the enemy.

Conventional Signs. The signs used for objects of military nature changed considerably during the war as the result of alteration of types of defensive and offensive works.