construction of scales:

=Problem No. 1.= The R. F. of a map is 1/1000. Required: 1. The
distance in miles shown by one inch on the map; 2. To construct a
graphical scale of yards; also one to read miles.

=Problem No. 2.= A map has a graphical scale on which 1.5 inches reads
500 strides. 1. What is the R. F. of the map? 2. How many miles are
represented by 1 inch?

=Problem No. 3.= The Leavenworth map in back of this book has a
graphical scale and a measured distance of 1.25 inches reads 1,100
yards. Required: 1. The R. F. of the map; 2. Number of miles shown by
1 inch on the map.

=Problem No. 4.= 1. Construct a scale to read yards for a map of R. F.
= 1/21120. 2. How many inches represent 1 mile?

=1865. Scaling distances from a map.= There are four methods of
scaling distances from maps:

1. Apply a piece of straight edged paper to the distance between any
two points, A and B, for instance, and mark the distance on the paper.
Now, apply the paper to the graphical scale, (Fig. 2, Par. 1862), and
read the number of yards on the main scale and add the number
indicated on the extension. For example: 600 + 75 = 675 yards.

2. By taking the distance off with a pair of dividers and applying the
dividers thus set to the graphical scale, the distance is read.

3. By use of an instrument called a map measurer, Fig. 4, set the hand
on the face to read zero, roll the small wheel over the distance; now
roll the wheel in an opposite direction along the graphical scale,
noting the number of yards passed over. Or, having rolled over the
distance, note the number of inches on the dial and multiply this by
the number of miles or other units per inch. A map measurer is
valuable for use in solving map problems in patrolling, advance guard,
outpost, etc.

[Illustration: Fig. 4]

4. Apply a scale of inches to the line to be measured, and multiply
this distance by the number of miles per inch shown by the map.

=1866. Contours.= In order to show on a map a correct representation
of ground, the depressions and elevations,--that is, the
undulations,--must be represented. This is usually done by
_contours_.

Conversationally speaking, a _contour_ is the outline of a figure or
body, or the line or lines representing such an outline.

In connection with maps, the word _contour_ is used in these two
senses:

1. It is a projection on a horizontal (level) plane (that is, a map)
of the line in which a horizontal plane cuts the