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Fire insurance maps are a core resource for documenting the development of neighborhoods over time. Founded in 1867, the Sanborn Map Company was the primary American publisher of fire insurance maps for nearly 100 years. They show lot numbers, square footage of lots, street addresses, which lots have buildings and their shape and materials. They indicate the type of construction, property lines, and the number of stories. They can narrow the date when a building was constructed. They can be used to track demolition, recent construction and alterations. They identify plot numbers necessary to access deed and other civil records.
Follow these steps to find your area of interest on the Sanborn Maps. For example, if you are interested in Washington, D.C. in 1939:
From the main page of the collection, select "Browse Maps" under the introductory paragraph. A series of drop-down menus will subsequently appear. The first menu asks users to select a state. Select District of Columbia.
Once you have selected District of Columbia, another drop-down menu will appear. Select a city from the drop-down menu. Click on Washington, D.C.
Clicking on the city reveals a date drop-down menu, which displays the editions produced for that city or town. Select your date; for our example select 1939 from the drop down menu. Selecting a date brings you to a screen depicting up to 25 images of the map sheets. To see more pages, click on the "Next" button at the bottom right of your screen, or, choose a specific map from the drop-down menu at the bottom center of the page.
Consult the edition's index map often called the "key," before searching for a particular urban location.
Index maps display the entire city (or the portion of the city contained within that volume) and label city blocks with numbers that correspond with their sheet number. Since there is no street name index, it is important that you have an idea as to where in a city your street or neighborhood of interest is located before you begin using the Sanborn Maps.
Index maps are always in the beginning of a map collection, so they are among the first sheets listed. They can be identified in the thumbnail collection as the only map that shows the entire city and the only map that also contains an atlas key. In our example, the Washington, D.C. index is sheet 0a.
The Library of Congress has been digitizing Sanborn Fire Insurance Maps in color and has made them available at the Geography and Map Reading Room website. Not all of the maps are available at this time but many of the earlier maps are online.