This datalayer is a polygon coverage displaying Major Watersheds throughout Massachusetts.
The data here were originally produced by MassGIS. MassGIS has produced a statewide digital datalayer of the 32 major watersheds covering Massachusetts. The datalayer is called WATRSHDS. Unlike the Major Drainage Basins layer, the watersheds in this layer extend beyond the state boundary to include the full extent of either the full watershed or a full USGS sub-basin.
MassGIS defines Watersheds (as well as Drainage Basins), using the USGS Water Resources Division definition, as "The land area drained by a river or stream."
Related terms are:
Drainage area: "The drainage area of a stream at a specified location is that area, measured in a horizontal plane, which is enclosed by a drainage divide." and,
Drainage divide: "Boundary between adjoining drainage basins"
This layer was derived from the Massachusetts Electronic Atlas (MEA) which was a collaborative project to provides access, via the Internet, to data about the Commonwealth, its thirteen regional planning agency districts and 351 cities and towns. This dataset is now only available via The Harvard Geospatial Library.
For more information on the original MassGIS datalayer please consult their website at: http://www.state.ma.us/mgis/watrshds.htm