How to Use a Fire Insurance Map to Research a Street Photo
By ImgHeal · Updated
A fire insurance map can help test a street or building identification through footprints, addresses, uses, and neighboring structures. Read the map's own symbols and date information first. Its colors are a cartographic code, not evidence of the building's painted appearance. Compare several site features and keep map information dates separate from the photograph's exposure date.
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Find the correct place and sheet
Use the map index to locate the candidate block and record the volume, sheet, edition, and revision notes. The Library of Congress explains that Sanborn maps were created for insurance purposes and require their keys for interpretation. Other map series have their own conventions. Do not assume a modern street number corresponds to the historical one without checking renumbering and the map's actual street relationships.
Compare features the map can support
Look at building footprint, adjoining structures, alley position, yard arrangement, and documented use. Compare these with the whole photograph, not just a favored façade. Map colors can encode construction categories rather than visible paint, and simplified shapes may not reproduce every architectural detail. Record the exact mapped evidence that supports or challenges the candidate. A symbol meaning a store does not identify its operator without another source.
Build a documented address link
Combine the map with dated directories or other reliable address records to test the proposed building and occupant. Preserve alternative locations and explain unresolved differences. Use changes between map editions cautiously, noting that revisions can lag events or contain updates. Keep the cited sheet and marked comparison in the research file, while a restored viewing image remains a derivative whose generated masonry, signs, or windows cannot authenticate the address.
Before using this evidence
- The exact sheet and key are consulted.
- Map coding is not confused with photographic color.
- Building and occupant claims have appropriate support.
Sources and further reading
- Library of Congress: Sanborn map overviewExplains the purpose, keys, symbols, and collection organization of fire insurance maps.
- Library of Congress: City and telephone directoriesIntroduces directories as sources for businesses, residents, addresses, and particular years.
Questions about this restoration task
Can I colorize a building from a Sanborn map's color?
Not as a record of paint color. The map's colors communicate cartographic categories defined by its key. Use documented color references for a color interpretation and label unsupported choices.
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