Sanborn maps, produced by the Sanborn Map Company, the primary American publisher of fire insurance maps for nearly 100 years, are valuable historical tools for urban specialists, social historians, architects, geographers, genealogists, local historians, planners, environmentalists, and anyone who wants to learn about the history, growth, and development of American cities, towns, and neighborhoods. They are large-scale plans containing information that was used to estimate the potential risk for urban structures. This information includes 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.
Textual information on construction details (for example, steel beams or reinforced walls) is often given on the plans while shading indicates different building materials. Extensive information on building use is given, ranging from symbols for generic terms such as stable, garage, and warehouse to names of owners of factories and details on what was manufactured in them. In the case of large factories or commercial buildings, even individual rooms and the uses to which they were put are recorded on the maps. Other features shown include pipelines, railroads, wells, dumps, and heavy machinery.
The Library of Congress has placed online nearly 25,000 Sanborn Fire Insurance Maps, which depict the structure and use of buildings in U.S. cities and towns. Maps will be added monthly until 2020, for a total of approximately 500,000. These maps are in color.
Sanborn maps for Delaware are also available on microfilm (Microfilm no. 3333, 3 reels). Later coverage for some Delaware cities is available on another reel of microfilm (Microfilm no. 5690).
Sanborn maps for several nearby states are also available on microfilm: District of Columbia (Microfilm no. 3338 and no. 4614), Maryland (Microfilm no. 3368 and no. 4741), New Jersey (Microfilm no. 3519 and no. 4612), and Pennsylvania (Microfilm no. 3332 and no. 4613).
NOTE: The original maps are color coded. The maps in this database and on microfilm (see above) are in black and white.