Sanborn Maps

Sanborn Maps was a creator and publisher of maps of US cities and towns. The Sanborn Maps were originally created for assessing fire insurance liability in urbanized areas in the United States. The maps include detailed information about buildings in approximately 12,000 US towns and cities. The maps are invaluable for documenting changes in the built environment of American cities over many decades. They are a highly useful resource for historical research, planning, preservation, genealogical research, sociological studies and research of urban geography.

The last Sanborn fire maps were published on microfilm in 1977, after US insurance companies stopped using maps for underwriting. The Sanborn Map Company continues on as a geospatial solutions company.

The Sanborn maps themselves are large-scale lithographed street plans at a scale of 50 feet to one inch (1:600) on 21 by 25 inches (53 by 64 cm) sheets of paper. The maps were published in volumes, bound and then updated until the subsequent volume was produced. Larger cities would have multiple volumes. In between published volumes, updates were sent out as correction slips. Subscribers would paste the slips on top of the old maps to reflect new or altered buildings or lots.

The map volumes contain an enormous amount of information. They are organized as follows: a decorative title page; an index of streets and addresses; a ‘specials’ index with the names of churches, schools, businesses etc.; and a master index indicating the entirety of the mapped area and the sheet numbers for each large-scale map (usually depicting four to six blocks); and general information such as population, economy and prevailing wind direction.

The maps include outlines of each building and outbuilding; the location of windows and doors; street names; street and sidewalk widths; property boundaries; fire walls; natural features (rivers, canals, etc.); railroad corridors; building use (sometimes even particular room uses); house and block number; as well as the composition of building materials including the framing, flooring, and roofing materials; the strength of the local fire department; indications of sprinkler systems; locations of fire hydrants; location of water and gas mains; and even the names of most public buildings, churches and businesses.

...
Wikipedia