What Is Meant by a Contour Interval on a Topographic Map?

What Is Meant by a Contour Interval on a Topographic Map?
A contour line represents a specific elevation above sea level. The interval between contour lines represents the difference in elevation between the two. Many different features in the land can be shown by the representation of contour lines and intervals.

Flat Land

If an area on a topographical map has no contour lines at all, or if the space between lines is extremely large, the map reader can deduce that the area is relatively flat.

Sloped Land

Contour lines at widely spaced intervals indicate a gentle slope in that area. Closely spaced contour lines indicate a steep slope.

Cliffs

If the contour lines are spaced at intervals so small that the lines are almost touching (or are actually touching), the map reader can construe that there is a cliff or cliffs in the area.

Valleys and Gullies, Ridges and Spurs

Contour lines that appear in a pattern shaped like a U indicate a gentle gully or rounded valley if the bottom of the U is facing in an uphill direction (look at the elevation numbers attached to the contour lines to figure out which way is uphill). If the Ushape is pointing downhill, it indicates a gentle ridge. Lines in a V shape mean a sharp, steep valley or gully if the V is pointing uphill, and a sharp ridge if it's pointing to lower elevation.

Cirques, Bowls and saddles

Contour lines that form a pattern in the shape of a half circle, like an amphitheater, indicate cirques or bowls. Hourglass configurations with higher contour elevations on each side represent a low point on a ridge, also known as a saddle, pass or col.

Value of Contour Intervals

Contour lines are marked, usually every five lines, and below the scale measurements on the map you'll find what the contour interval is. It is common, for example, for a map to say that contour intervals are 40 feet and that any dotted contour lines represent 20-foot contours.

Article Written By Naomi Judd

Naomi M. Judd is a naturalist, artist and writer. Her work has been published in various literary journals, newspapers and websites. Judd holds a self-designed Bachelor of Arts in adventure writing from Plymouth State University and is earning a Master of Fine Arts in creative writing from the University of Southern Maine.

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