Description: MassGIS has produced a statewide digital datalayer of the approximately 2300 sub-basins as defined and used by the USGS Water Resources Division and the Mass Water Resources Commission and as modified by Executive Office of Environmental Affairs (EOEA) agencies. These sub-basins were aggregated together to make the 28 basins of the Major Basins Datalayer . Cape Cod and the Islands do not have much lateral 'surface' drainage because the soils are so porous. The sub-basin line shown for Cape Cod is the approximate groundwater divide between Cape Cod Bay, Vineyard Sound, and the Atlantic Ocean, taken from sub-surface groundwater contours. The state coastline and boundaries are included in the sub-basin coverages and are differentiated by arc attributes.