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From Fire Hazards to Family Trees: The Sanborn Fire Insurance Maps

Created for US insurance firms during a period of devastating fires across the 19th and 20th centuries, the Sanborn maps blaze with detail — shops, homes, churches, brothels, and opium dens were equally noted by the company’s cartographers. Tobiah Black explores the history and afterlife of these maps, which have been reclaimed by historians and genealogists seeking proof of the vanished past.

But a combination of dense concentration, shoddy construction, poor regulation, and inadequate firefighting services meant that fires in the period of swift industrialization from roughly the end of the Civil War to the Great Depression were particularly destructive. These maps used an elaborate system of color coding, symbols, and abbreviations to indicate a dizzying amount of information — from building materials to street widths; from locations of standpipes to the presence of flammable chemicals; from the height of a structure to the number of skylights. For a variety of reasons — consolidation in the insurance business, complacency because of their perceived monopoly, more sophisticated methods for assessing fire risk, and new forms of data storage that made the huge, heavy Sanborn atlases increasingly obsolete — the company’s profits had dropped to $100,000 a year by the late 1950s.

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