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Line Style, Abbreviations & Modern Symbols

Line Style

Much information could be conveyed through line types. A solid line indicated a solid wall. A break in a line showed doorways and other passages. Additionally, dashed lines could indicate some aspect of wall construction or the presence of a mansard roof. Extending solid lines beyond the edge of a building was a technique for indicating how high above the roof fire walls were built. When interpreting any fire insurance map, researchers should take care to consult the legend for that particular edition to ensure the correct interpretation of line symbology.


Fire insurance maps often relied on abbreviations to convey the type of activity that took place in a structure, since that information had some bearing on the likelihood of fires. The most common abbreviations are as follows: "D" or "Dwg" for a dwelling, "F" for a flat or apartment, "S" for a store, "Sal" for a saloon. Other abbreviations added more information about a structure: numerals were used to indicate the number of stories in a building, and the letter "B" indicated the presence of a basement. These could be combined, so that "2B," for instance, indicates that a building has two stories and a basement. Multiple symbols for a single structure could reflect the use or nature of different parts of a building; hence a two-story building with a basement might be marked "2B" for the main portion of the structure while an addition on the front had the number "1" by itself to indicate a single story.

In some instances, symbols and abbreviations were combined with text to describe a specific use. These can be frequently difficult to interpret because they are run together; the symbols for store and basement, for instance, can be combined in the form SinB, representing the phrase "store in basement."

Modern Symbols for Fire Insurance Maps

The symbolization used on fire insurance maps evolved over time as a result of such factors as the consolidation of the industry under the control of the Sanborn Map Company, the development and improvements of building codes, the development of larger and taller buildings that required notation of special features, and the maturation of this form of cartographic endeavor. To aid researchers in using these maps, a series of keys or legends have been reproduced from reference manuals that the Sanborn Map Company produced for its employees. Researchers, should not rely solely on the extensive legends reproduced here, however, the legends published in the atlases and on the small editions issued as loose sheets represent the use of symbols at the time the map was made.

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  March 23, 2022
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