Sanborn Maps were originally created for assessing fire insurance liability in many areas of the United States. The maps include detailed information regarding town and building information in approximately 12,000 U.S. towns and cities from 1867 to 1970. They are a very useful resource for historical research, planning, preservation and genealogical research.

1909 Richmond Indiana Sanborn Collection Cover
The Sanborn Company began making fire insurance maps in 1867 when founded by Daniel Alfred Sanborn, a surveyor from Massachusetts. The Sanborn Map Company created maps for fire insurance assessment in the U.S. and within several decades became the largest and most successful American map company.
The Sanborn maps are large-scale lithographed street plans at a scale of 50 feet to one inch (1:600) on 21 inch by 25 inch sheets of paper. The maps were created in volumes, bound and then updated until the subsequent volume was produced. Larger cities would have multiple volumes. In between volumes, updates (new drawings of new or altered buildings or lots) were created and sent out to be pasted on top of the old maps (referred to as ˜slips™) to reduce expense and preserve accuracy.
The 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 companies.
The Morrison Reeves Library has a bound collection of Sanborn maps for the City of Richmond.
Here’s an example of a local Sanborn Map for an Industrial Property located on South O Street, Richmond.

Former Automotive Gearworks Building, Richmond Indiana.
These maps are extremely useful for all researchers and genealogy. They’re also a great resource for determining previous use and the age of buildings, and adjacent property information.
For more on this subject see: Text Source: http://en.wikipedia.org/wiki/Sanborn_Maps