Map sketching is an important factor in trench warfare to-day as it is in a war of movement. A fairly accurate map will indicate more than many words and in much less time. Time is the great factor in war. Instruction must also be rapid. Here are ten lessons which would occupy a week if taken morning and afternoon. The aim of the instruction as in company rifle shooting is to train many men to do a satisfactory job, not to make a few finished topographers. Neatness, accuracy and initiative are cardinal points.
For the instructor, reference should be made to Grieves' "Military Sketching and Map Reading", 2nd edition, if he desires to supplement any points given here.
LESSON 1. (CLASS ROOM—FOUR HOURS.)
Problem—Map Reading.
Study the conventional signs found in the "Manual for Non-commissioned Officers and Privates of Infantry of the Army of the U.S.," 1917, page 273, or in Grieves, pages 28-35. These conventional signs are not universal and must be used only as indications of the general practice.
In map sketching in the field few conventional signs are used, and the items of importance are written on the map, such as WOODS, CULTIVATED, HEDGE, SWAMP, etc.
TAKING UP MAP SCALES.—There are three ways of indicating the relation between the actual distance on the ground and the space the same distance occupies on the map:
1. The graphic scale is a straight line divided into units, as miles, yards, feet or meters, which represents the actual ground distance. Thus if 6" = 1 mile the line would be six inches long and marked at one end and 1 mile at the other, three inches being marked ½ mile, etc. It is important to always have this graphic scale on a map so that if the paper gets wet or is stretched from its original size the scale will change in the same proportion.
2. A Statement in words or figures, e.g., 3 inches equal one mile, meaning that 3 inches measured anywhere on the map represent 1 mile on the actual ground.
3. The Representative Fraction (generally known abbreviated as R.F.) having a number above the line that shows the unit length on the map and below the line the number of units which are in the corresponding actual ground distance. For example, if 1" = 1 mile, then the R.F. is: