|Sanborn maps for PA towns and cities|
Maps made by the Sanborn Company provide a great opportunity to see the block by block, building by building development of a community. They offer an incredible level of detail (number of floors, roofing materials, wall construction, location of hydrants and water lines, etc. etc. etc.) as well as the actual "footprint" of each building. The maps were updated every few years, so by comparing them, you can see exactly how your community changed in the late 19th and early 20th centuries.
This digital collection at the Penn State's Paterno Library has great, high-quality images for browsing and downloading.
A great PRIMARY source!