What is a topographic map?

[music fades in]

Welcome to CoreFacts, where we're always short on time and big on science. I'm Jessica Robertson. Today we have a question about maps.

What is a topographic map?

First let me point out that a map is a representation of the Earth, or part of it. The distinctive characteristic of a topographic map is that the shape of the Earth's surface is shown by contour lines. So, what exactly is a contour line? Contours are imaginary lines drawn on a map that join points of equal height.

Imagine walking along the beach. As you walk across the sand on the shore, your elevation stays constant. That path is drawn by one contour line. Now imagine walking from the shoreline into the ocean where the ground is below sea level. That path, which follows a different elevation than when you were walking on the shore, is drawn by a different contour line.

This can help measure depths of the ocean bottom, the height of mountains, and the steepness of slopes. A topographic map shows more than contours. These maps also include symbols that represent features such as streets, buildings, streams, and woods.

And now you know. Join us again every weekday for a new CoreFact. For other CoreFacts, or for CoreCast, our in-depth science podcast, go to usgs.gov/podcasts. If you'd like to have a question featured on our show, give us an email at corefacts@usgs.gov or a phone call at 703-648-5600. Remember, long distance fees do apply.

CoreFacts is a product of the U.S. Geological Survey, Department of the Interior.

[music fade out]