1. Look for the water courses, that is the drainage system. It will give the general slope of the land.
2. Look for the high points between the water courses, remembering that there is always a valley then a hill then a valley again continued in succession.
3. Finally locate towns, railroads, main highways and work down to the minor details.
In measuring a map to get the actual distances on the ground, copy the graphic scale on any piece of paper and apply this directly or if your distances exceed your scale use the edge of a piece of paper and then apply it to the graphical scale on the map.
Lesson 2. (Field Work—five Hours.)
Problem—Stride Scale Map Making.
Producing a map from the actual ground requires certain instruments. The second lesson takes up the preparation of the stride scale on the alidade and the different kinds of maps, made in military sketching.
The alidade is a triangular ruler with one or more working scales on it beside other measurements. The working scale is, for infantry, the stride or the space of ground covered from left foot to left foot again in walking, reduced to the proper map distance. This varies with individuals of course. Any scale of units, however, can be used as, horse trot, telegraph poles, etc.
The working scale for each man is made by having him step off a measured course, say 440 yards. The ground should not be too even as a general average is needed, moreover the pace must be the natural gait of the individual under ordinary circumstances. Let him count the course three times then average the three results for the final estimate.
Now to convert this into a working scale for the alidade made on a scale of six inches to the mile; take the case of a man who takes 220 strides in 440 yards: