Topographic Maps

What is a USGS Topographic map?

A topographic map is a unique map that shows the shape of the Earth's surface using contour lines. The contours make it possible to measure the height of mountains, depths of water bodies, or the steepness of slopes. The U.S. Geological Survey is the government agency tasked with producing these maps. These maps can prove quite useful to the hydrology program, especially in the west where the unique terrain is a forecasting issue.

Topographic maps are on the scale of 1:24,000 (1 inch = 2,000 feet). They are also known as 7.5 minute quadrangles, because they show an area that spans 7.5 minutes of latitude by 7.5 minutes of longitude. This scale allows for considerable detail to be shown. It takes approximately 57,000 1:24,000 scale maps, to cover the conterminous U.S., Hawaii, and territories.

How can a topographic map help the Hydrologic Program Manager?

w Provides a quick way to look at the type of terrain that is in an area where hydrologic problems may be possible.

w Can help a new Hydrologic Program Manager become familiar with the HSA.

w When site visits are not possible, for whatever reason, a topographic map can at least provide a visual picture of what type of terrain an area may be surrounded by.

w Can be useful in the preparation of E-19s.

w Can be used for establishing river cross sections, for pre-event dam break analysis.

w Provides a means for delimiting approximate flood stages and coarse inundation impacts, when other information is unavailable.

There are numerous sources of electronic topographic maps available, both on the internet and from private companies. Your office may have decided to use a different type of electronic topographic map, than the sources mentioned above. Whatever type of map your office uses, it is ideal for the Hydrologic Program Manager to be familiar with it.

map showing height near Jefferson Forest