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:

440 yards = 15,840 inches
15,840 / 220 = 72, or his stride in inches
then 880 strides = 1 mile or 6" on the scale.

It is better to have a scale of 1,000 strides which is easily done by
the proportion:

1,000 sts. : 880 sts. : : x : 6
x = 6.8

now draw a line 6.8 inches long and a diagonal line from it; divide
this diagonal line into 10 equal parts for each 100 paces at any
convenient scale and draw a line from the end of the tenth part to the
end of the 6.8 inches line; draw lines parallel to this line from each
of the divisions. The 6.8" line is then divided into 10 equal parts;
each of these parts may be divided in the same manner into tenths.

Your scale is ready to be pasted or transferred to the alidade and
each 6.8. inches on the map will equal 1,000 of your strides on the
ground, or about 1-1/12 miles (2,000 yards).

There are two general classes of sketches:

1. ROAD SKETCH.--A traverse (passing over) made along a definite rout
showing all features of military importance for a distance of 200 or
300 yards on each side of the road. A road sketch is always made on a
scale of 3 inches to 1 mile.

2. AREA SKETCH.--A map of a definite locality. There are 3 kinds of
area sketches according to opportunity for observation:

(a) Position Sketch--when access may be had to the whole area.
(b) Outpost Sketch--where part of the ground must be mapped without
passing over it. This form is applicable particularly to trench
warfare. Intersection and resection are used to locate points