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1:2,000,000-Scale Hydrologic Unit Boundaries |
What this map layer shows:
The boundaries of natural and manmade stream-drainage areas. Included
are the boundaries of 2,264 watersheds.
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![opens the U.S. Geological Survey home page](https://webarchive.library.unt.edu/eot2008/20090507193739im_/http://www.nationalatlas.gov/images/LOGOS/MLD/logo_usgs.gif) |
Background Information |
Sample Map
Hydrologic units are used for collecting and organizing hydrologic data. These units are land areas that catch rain or snow and drain to marshes, streams, rivers, lakes, or ground water. The hydrologic unit system divides and subdivides the United States into four nested levels of units. The largest units are called regions and represent either the drainage area of a major river, such as the Missouri region, or the combined drainage areas of a series of rivers, such as the Texas-Gulf region, which includes numerous rivers draining into the Gulf of Mexico. The successively smaller units within regions are subregions, accounting units, and cataloging units. Cataloging units are also known as watersheds. This map layer was compiled by the U.S. Geological Survey.
The 1:2,000,000-Scale Hydrologic Unit Boundaries map layer shows the boundaries
of 2,264 cataloging units within the United States, Puerto Rico, and the U.S.
Virgin Islands. The hydrologic units outlined in this map layer represent natural
and manmade stream-drainage areas. Descriptive information includes names and
codes for the cataloging units, accounting units, subregions, and regions. Further
information on hydrologic units is available from the USGS
Water Resources Hydrologic Unit Maps page.
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![](https://webarchive.library.unt.edu/eot2008/20090507193739im_/http://www.nationalatlas.gov/images/common/transparent.gif) |
![](https://webarchive.library.unt.edu/eot2008/20090507193739im_/http://www.nationalatlas.gov/images/common/transparent.gif) |
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