This data set contains digital hydrologic unit boundaries at the subwatershed (12-digit) level. The data set was developed by delineating the boundary lines on base maps or overlays and digitizing the delineated lines. Digital Elevation Model data may have been used in part of the process to establish preliminary boundaries. This data set consists of geo-referenced digital map data and attribute data. The map data include complete coverage of the entire state including those subwatersheds crossing the borders of adjoining states. The digitized hydrologic units provide area extent of drainage patterns at the appropriate level of detail (basin, subbasin, watershed and subwatershed). Each polygon is linked to a set of attributes, including the hydrologic unit code and information on acreage, type, non-contributing area and trans-basin flow.