Maps pertaining to surface water (historically and currently) in Philadelphia, and the city's water supply and sewerage systems. The site also provides links to many scanned, old atlases, topographical maps, etc. for Philadelphia (including some complete atlas volumes), nearby communities, and counties in southeastern Pennsylvania.
Aerial photography of Philadelphia, the Delaware Valley, and the Mid-Atlantic region produced by the Dallin areial Survey Co., 1924-1941.
Accessible via the Hagley Museum & Library's Hagley Digital Archives.