3. RELIEF. Relief is the representation of the shape

and height of landforms and the characterization of the

surface of the earth.

The elevation of points and the relief of an area

affect the movement and deployment of units by

limiting the route of travel, their speed of movement,

and the ease or difficulty of attacking or defending an

area. Also relief affects observation, fields of fire,

cover, concealment, and the selection of key terrain

features.

There are several ways of indicating elevation and

relief on maps. The most common way is by contour

lines. A CONTOUR LINE is a line representing an

imaginary line on the ground along which all points are

at the same elevation.

Contour lines indicate a vertical distance above

or below a datum plane. Starting at sea level,

normally the zero contour, each contour line

represents an elevation above sea level. The

vertical distance between adjacent contour lines is

known as the CONTOUR INTERVAL. The amount

of the contour interval is given in the marginal

information. On most maps, the contour lines are

printed in brown. Starting at zero elevation, every

fifth contour line is drawn with a heavier line.

These are known as INDEX CONTOURS.

Someplace along each index contour, the line is

broken and its elevation is given. The contour lines

falling between index contours are called

INTERMEDIATE CONTOURS. They are drawn

with a finer line than the index contours and,

usually, do not have their elevations given.

crossed multiplied by the contour interval is the distance

above or below the starting value.

Using the contour lines on a map, you may

determine the elevation of any point as follows:

When the desired point is on a contour line, its

1. Find the contour interval of the map from the

elevation is that of the contour.

marginal information, and note both the amount and the

For a point between contours, most military needs

unit of measure.

are satisfied by estimating the elevation to an accuracy

2. Find the numbered contour line (or other given

of one half of the contour interval. All points less than

elevation) nearest the point for which the elevation is

one fourth of the distance between the lines are

being sought.

considered to be at an elevation of one half of the contour

3. Determine the direction of slope from the

interval above the lower line (fig. 5-6).

numbered contour line to the desired point.

To estimate the elevation of the top of an unmarked

4. Count the number of contour lines that must be

hill, add half of the contour interval to the elevation of

crossed to go from the numbered line to the desired point

and note the direction-up or down. The number of lines

the highest contour line around the hill.