Figure 8-18.-Typical contour formations.
CHARACTERISTICS OF CONTOUR LINES
A contour line is a line of equal elevation; therefore,
two different lines must indicate two different
elevations. So two different contour lines cannot
intersect or otherwise contact each other except at a
point where a vertical or overhanging surface, such as a
vertical or overhanging face of a cliff, exists on the
ground Figure 8-18 shows an overhanging cliff. You
can see how the segments of contour lines on this cliff
are made as dotted (or hidden) lines. Aside from the
exception mentioned, any point where two different
contour lines intersect would be a point with two
different elevations-an obvious impossibility.
In forming a mental image of the surface
configuration from a study of contour lines, it is helpful
for you to remember that a contour line is a level line;
that is, a line that would be formed by a horizontal plane
passing through the earth at the indicated elevation. If
you keep this concept of levelness in mind you can
usually get the feel of the rise and fall of the ground
as you study the contour lines on the map.
A contour line must close on itself somewhere
either within or beyond the boundaries of the map. A line