Contour Lines

Contour lines are what allow topographic maps to show the three-dimensional configuration (i.e., topography) of the Earth’s surface. Sea level is accepted worldwide as the zero contour line, so that elevation measurements are given in terms of either feet or meters above or below sea level.

Rules for Contour lines:

1. Every point on a contour line is the same elevation; contour lines connect points of equal elevation.

2. Contour lines are always a uniform vertical distance apart, called a contour interval, which is stated on the map (bottom middle).

3. Contour lines never branch, fork, or cross one another.

4. Contour lines form a “V” when crossing a stream valley; the bottom of the “V” always points upstream, so the water flows in the opposite direction.

The V points upstream, south in this case.   So the stream is flowing north.

5. Every 5^th contour line, called an index contour, is drawn darker to aid in counting the lines.

6. Dotted contour lines, called supplementary contours, are used to show more detail in an area of little relief (areas that are flatter).

7. Hachured contour lines indicate a closed depression.   The hachures are located on the downhill side.

8. Closely spaced contour lines represent a steep slope (higher gradient), while widely spaced contour lines represent a gentle slope (lower gradient).

The image below is of a portion of a topographic map, answer the following questions using this map.

The Stream, Bear Hole Run, has many contour lines that cross it. Where they cross, the contour lines form Vs. The stream flows in the opposite direction of the stream.