Fig. 8
Fig. 9
[1884]. Form lines. It frequently happens that a sketch must be made very hastily and time will not permit of contouring. In this case form lines are used. These lines are exactly like contours except that the elevations and forms of the hills and depressions which they represent are estimated and the sketcher draws the form lines in to indicate the varying forms of the ground as he sees it.
[1885]. Scales. The Army Regulations prescribe a uniform system of scales and contour intervals for military maps, as follows:
Road sketches and extended positions; scale 3 inches to a mile, vertical (or contour) interval, 20 feet.
Position or outpost sketches; scale 6 inches to a mile, vertical (or contour) interval, 10 feet.
This uniform system is a great help in sketching as a given map distance, [Par. 1867a], represents the same degree of slope for both the 3 inch to the mile or the 6 inch to the mile scale. The map distances once learned can be applied to a map of either scale and this is of great value in sketching.