By looking through various historic city atlases and aerial photographs in the Map Collection, the construction date of a house can usually be determined within a ten or fifteen year time span.
The Map Collection is a depository for U.S.G.S. topographic maps for all states, Puerto Rico and the U.S. Virgin Islands
The Map Collection maintains historical Sanborn mapping for Pennsylvania, New Jersey, Maryland and Delaware. Sanborn mapping for Philadelphia is historical and current
Because neighborhoods are not defined by ordinace, boundary streets are open to debate. The Map Collection uses various historical sources to identify specific neighborhoods and deliniate boundaries
The Map Collection has a series of Main Line railroad atlases, from the 1880s to the 1980s, that indicate land holdings and estate names