Maps in the US Library of Congress

[PeterC]

The US Library of Congress has over 400,000 US maps, of which thousands are online, and many of which are downloadable in various formats.

A useful resource for OPS are Sanborn Fire Insurance Maps, produced as part of the Sanborn Maps. As they say The Sanborn Fire Insurance Maps are a valuable resource for genealogists and historians, covering all the states from the late 1880s through the early 1960s.