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This data set is a complete digital hydrologic unit boundary layer of the Subbasin (8-digit) 4th level for the entire United States. This data set consists of geo-referenced digital data and associated attributes created in accordance with the "Federal Guidelines, Requirements, and Procedures for the National Watershed Boundary Dataset; Chapter 3 of Section A, Federal Standards, Book 11, Collection and Delineation of Spatial Data; Techniques and Methods 11-A3" (04/01/2009). http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/water/watersheds/?cid=nrcs143_021630 . Polygons are attributed with hydrologic unit codes, name, and size. The data is currently updated through the USGS National Hydrography Dataset (NHD) Program and replicated to NRCS twice per year. The U.S. Fish and Wildlife Service (USFWS)modified this version of the dataset by deleting some fields, reprojected the data to an Albers equal area projection and recalculated the 'AreaAcres' field. Those Subbasins that did not extend to NOAA's 3 Nautical Mile Line were extended by the USFWS to meet this boundary to provide consistency across Subbasins, and Subbasins were created for the Rota, Tinian, and the Palmyra Atoll. |