meaning that 3 inches measured anywhere on the map represent 1 mile on
the actual ground.

3. The Representative Fraction (generally known abbreviated as R.F.)
having a number above the line that shows the unit length on the map
and below the line the number of units which are in the corresponding
actual ground distance. For example, if 1" = 1 mile, then the R.F. is:

1" (map distance)
-----------------------------------
63,360" (1 mile--ground distance)

if 3" = 1 mile the R.F. is:
3" (map distance) 1
----------------------------------- or -------
63,360" (1 mile--ground distance) 21120

if 6" = 1 mile:
6" 1
-------- or -------
63360" 10560

if 12" = 1 mile:
12" 1
--------- or ------
63360" 5280

In reading a map one must know the scale and also where the North is.
This is always indicated by an arrow pointing either to the magnetic
North or the true North. If to the magnetic North the needle will have
but one barb away from the true North. The angle between the magnetic
and the true North is the declination.

Placing the map in proper relation to the ground so that points of the
compass coincide on map and ground is called _orienting the map_.

In map work there is one vital point to remember; practically all the
ground surface is in its present form as a result of water action

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.