Sanborn Keys, Legends, and Symbol Sheets

Fire insurance maps are distinctive because of the sophisticated set of symbols that allows complex information to be conveyed clearly. In working with insurance maps, it is important to remember that they were made for a very specific use, and that although they are now valuable for a variety of purposes, the initial selection of information to be mapped and the way that information was portrayed was dictated by the needs of the insurance industry.

Key for interpreting Sanborn fire insurance maps

The prefatory material found at the beginning of atlases and on the first sheet of smaller editions usually included a legend or "key" to symbols. Knowledge of these is essential to proper interpretation of the information found in fire insurance maps. The use of these symbols on fire insurance maps, especially those done by the Sanborn Map Company, was prescribed by company manuals and can usually be interpreted with a considerable degree of confidence. However, the symbols, abbreviations, and annotations are not always easily interpreted. Therefore, it is important for researchers to consult the keys to symbols. It is also important to remember that over time new symbols were added and that there were variations in the way in which symbols were applied.