Topographic Maps and Contour Lines
Tips for understanding contour lines.
When first looking at a topographic map, it may appear somewhat confusing and
not very useful.
There are a few rules that topographic contours must obey, however, and once
you understand these rules the map becomes an extremely useful and easy to
use tool.
The rules are as follows:
1) Contour lines are brown. Every point on a contour line represents the exact
same elevation.
As a result of this every contour line must eventually close on itself to form an
irregular circle.
Contour lines on the edge of a map do not appear to close on themselves
because they run into the edge of the map, but if you got the adjacent map you
would find that, eventually, the contour will close on itself.
2) Contour lines can never cross one another. They join places of the same
elevation above sea level.
Each line represents a separate elevation, and you can’t have two different
elevations at the same point.
The only time two contour lines may merge is if there is a vertical cliff.
3) Moving from one contour line to another always indicates a change in
elevation. The elevation of some lines must always be shown.
4) The closer contour lines are to one another, the steeper the slope is in the real
world.
If the contour lines are evenly spaced it is a constant slope, if they are not evenly
spaced the slope changes.
5) A series of closed contours (the contours make a circle) represents a hill.
6) Contour lines crossing a stream valley will form a "V" shape pointing in the
uphill (and upstream) direction.