Founded in 1867 by D. A. Sanborn, the Sanborn Map Company was the primary American publisher of fire insurance maps for nearly 100 years.
Sanborn maps were created to assist fire insurance companies as they assessed the risk associated with insuring a particular property. They include information such as the outline of each building, the size, shape and construction materials, heights, and function of structures, location of windows and doors. The maps also give street names, street and sidewalk widths, property boundaries, building use, and house and block numbers.
source: ProQuest Digital Sanborn Maps