Figure 5-18.--Slope diagram.
Figure 5-20.--Measuring curved line distance on a map.
indicated by a special scale legend that is printed on the
map. The second type of scale is the ratio between the
horizontal distance on the map and the corresponding
distance on the ground.
The GRAPHIC SCALE that is printed on your
map is especially made for that map and should not
Figure 5-19.--Graphic scale.
be used on any other map. Figure 5-19 shows a typical
graphic scale. To the right of the zero (0), the scale is
marked in full units of measure and is called the
affected by the slope of the ground. Most equipment
PRIMARY SCALE. The part to the left is zero (0) and
has a limit on the steepness of slope it can negotiate.
is divided into tenths of a unit and is called the
So a more exact way of describing a slope is
EXTENSION SCALE. Most maps have three or more
demanded. Slope may be expressed in several ways,
graphic scales, each of which indicates distance in a
but all of them depend upon a comparison of vertical
different unit of measure. To determine the
distance (VD) to horizontal distance (HD) (fig. 5-18).
straight-line distance between two points on a map,
VD is the difference between the highest and lowest
use the following steps:
elevations of the slope and is determined from the
contour lines. HD is the horizontal ground distance
1. Lay the straightedge of a piece of paper on the
between the highest and the lowest elevations of the
map so the edge of the paper touches both points.
slope.
2. Make a mark on the edge of the paper at each
point.
The VD and HD must be expressed in the same
units. Both measurements must be made with extreme
3. Move the paper down to the graphic scale, and
accuracy in order to have a valid determination of
from the scale, read the ground distance between the
steepness. The computations normally are made for only
points. Be sure to use the scale that indicates the unit of
the steepest part of a slope.
measure desired.
To measure distance along a winding road, stream,
Scale and Distance
or other curved line, the straightedge of a piece of paper
should be used again.
A map is a graphic representation of an area and,
1. Make a mark at or near one end of the paper and
therefore, is not made to full scale (actual size). Since it
place it at the point from which the line is to be
is not full size, some means of measuring the distance
measured, as shown in figure 5-20.
from one point on the map to another is necessary. This
is done with the aid of a scale.
2. Align the edge of the paper along a straight
There are two types of scales in general use on
portion, and make a tick mark on both the map and the
military maps. The first is called a graphic scale and is
paper at the end of the aligned portion
5-15
