Sanborn maps are special maps produced to assist insurance companies in determining risk and setting rates. The maps show the location, occupancy, and construction of commercial buildings within a town.
Reading the maps generally require some mastery of the key. For an example the Bank Building is 2 story with a composition roof with a 12 inch fire wall. Each interior floor has a 12 foot ceiling and the building is 26 foot wide (see 1926 map).