Library of Congress has placed online nearly 25,000 Sanborn Fire Insurance Maps, which depict the structure and use of buildings in U.S. cities and towns. Maps will be added monthly until 2020, for a total of approximately 500,000. The online collection now features maps published prior to 1900. By 2020, all the states will be online, showing maps from the late 1880s through the early 1960s. As the LofC website explains,
The Library also has a thorough explanation of the maps and how to search for them and understand their keys and color schemes. Additional examples were included in one of the Library's recent blog posts.
The Sanborn Fire Insurance Maps are a valuable resource for genealogists, historians, urban planners, teachers or anyone with a personal connection to a community, street or building. The maps depict more than 12,000 American towns and cities. They show the size, shape and construction materials of dwellings, commercial buildings, factories and other structures. They indicate both the names and width of streets, and show property boundaries and how individual buildings were used. House and block numbers are identified. They also show the location of water mains, fire alarm boxes and fire hydrants.