n drawing on the map lines that
represent the lines of sight to known and visible places. The
lines pass through the map position of the places you see and
are parallel to the actual lines of sight; therefore they are the
map representations of the lines of sight, and their intersection
is the map position of the eye of the observer.

After this orientation and location of position, one can deduce
from the map everything there is to know in regard to directions.
In this respect, study of the ground itself will show no more
than will study of the map.

After "What direction?" comes "How far?" To answer this, one
must understand that the map distance between any two points
shown bears a fixed and definite relation or proportion to the
real distance between the two points.

For instance: We measure on a map and find the distance between
two points to be 1 inch. Then we measure the real distance on
the ground and find it to be 10,000 inches; hence the relation
between the map distance and the real distance is 1 to 10,000,
or 1/10000. Now, if the map is properly drawn, the same relation
will hold good for all distances, and we can obtain any ground
distance by multiplying by 10,000 the corresponding map distance.

This relation need not be 1/10000, but may be anything from 1/100
that an architect might use in making a map or plan of a house up
to one over a billion and a half, which is about the proportion
between map and real distances in a pocket-atlas representation of
the whole world on a 6-inch page. Map makers call this relation
the "scale" of the map and put it down in a corner in one of
three ways.

First. 1 inch equals 100.

Second. 1/100.

Third. As shown in figure 3 (section 1).

These expressions mean one and the same thing. A variation of
the first method on a map of different scale might be: 1 inch
equals 1 mile. Since a mile contains 63,360 inches, then the
real distance between any two points shown on the map is 63,360
times the map distance.

To find the ground distance by the third kind of scale, copy it
on the edge of a slip of paper, apply the slip directly to the
map, and read off the distance; and so we answer the question,
"How far?"

After direction and distance comes the interpretation of the
signs, symbols, and abbreviations on the map. Those authorized
are given in section 2 (a reprint of Appendix 4, Field Service
Regulations, 1914); but there are a good many other conventional
sig