1999. United States Geological Survey (USGS)U.S. Environmental Protection Agency. The National Hydrography Dataset (NHD) is a feature-based database that interconnects and uniquely identifies the stream segments or reaches that c... State of Pennsylvania.
1996. Water Department - Information Systems & Technology. Planimetric Coverage containing the delineation of topographic contours. Annotation of Contour Line elevations exists. Annotation viewable at 1" = ... City of Philadelphia, Pennsylvania.