Beginning in 1867, the Sanborn Map Company produced its fire insurance maps to provide uniform and detailed information about the built environment to insurance companies for the purposes of risk assessment. These large-scale color maps, indicate the dimensions, construction, and function of buildings, and also show features such as property boundaries, street names, and house and block numbers. Sanborn fire insurance maps are therefore an excellent source of information about urban development in American cities in the later 19th and the 20th centuries.
For more information on the history of fire insurance maps and the Sanborn Company as well as on the collection of the Library of Congress and other libraries with fire insurance map holdings, see the preface and introduction to Fire Insurance Maps in the Library of Congress: A Checklist, found on the UC Berkeley Library website or in print at the UM Clark Library (Z 6026 .I7 U541).
Note: Most updated versions of Sanborn and other fire insurance maps are original editions with pasted-on correction slips. In such cases, the date of the information is usually a penciled date contained in a corrections box at the beginning of the set or volume, rather than the date appearing on the title sheet.