Digitized boundaries of 104 major watersheds defined in the Pennsylvania state water plan. The State Water Plan, originally developed in the 1970s, divided Pennsylvania's major river basins into 20 smaller units (subbasins) for planning purposes. Most of these subbasins are further divided into watershed areas (designated 'A', 'B', 'C' etc.) that range in size from about 100 to 1000 square miles.