When you pick up a map, the first question is, Where is the north?
This can usually be told by an arrow (see fig. 1, section 1)
which will be found in one of the corners of the map, and which
points to the true north--the north of the north star.

On some maps no arrow is to be found. The chances are a hundred
to one that the north is at the top of the map, as it is on almost
all printed maps. But you can only assure yourself of that fact
by checking the map with the ground it represents. For instance,
if you ascertain that the city of Philadelphia is due east of
the city of Columbus, then the Philadelphia-Columbus line on
the map is a due east-and-west line, and establishes at once all
the other map directions.

Now, the map represents the ground as nearly as it can be represented
on a flat piece of paper. If you are standing up. facing the
north, your right hand will be in the east, your left in the
west, and your back to the south. It is the same with a map;
if you look across it in the direction of the arrow--that is,
toward its north--your right hand will be toward what is east
on the map; your left hand to the west; the south will be at
the bottom of the map.

There is another kind of an arrow that sometimes appears on a
map. It is like the one in figure 2, section 1, and points not
to the true north but to the magnetic north, which is the north
of the compass. Though the compass needle, and therefore the arrow
that represents it on the map, does not point exactly north, the
deviation is, from a military point of view, slight, and appreciable
error will rarely result through the use of the magnetic instead
of the true north in the solution of any military problems.

[Illustration: Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5.]

Should you be curious to know the exact deviation, consult your
local surveyor or any civil engineer.

Both arrows may appear on your map. In that case disregard the
magnetic arrow unless you are using the map in connection with
a compass.

If a map is being used on the ground, the first thing to be done
is to put the lines of the map parallel to the real outlines of
the ground forms, and roads, fences, railroads, etc., that the
map shows; for the making of a map is no more than the drawing
on paper of lines parallel to and proportional in length to real
directions and distances on the ground.

For instance, the road between two places runs due north and south.
Then on the map a li