GIS Map Gallery: April 2004
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A watershed is an area of land that drains precipitation to a common area. Watersheds can be depicted at a variety of scales. The largest of which, basins, cover broad areas. Within Virginia, water eventually flows into one of 4 places: the Ohio River, the Tennessee River, the Chesapeake Bay, or the Atlantic Ocean. Within these basins are major river drainages. The main map shows the 13 major river drainages in Virginia. River drainages can be subdivided further into Hydrologic Units also known as 8-digit HUCs (Hydrologic Unit Codes), not shown on the map. They are called 8-digit HUCs because their labels are made-up of a series of 8 numbers. These Hydrologic Units can then be further subdivided into subwatersheds or 14-digit HUCs, which are even smaller. The subwatersheds or 14-digit HUCs are shown for the Holston River Watershed. Watersheds could be divided further, based on progressively smaller streams.
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