If you've ever wondered what your block looked like 100 years ago, Sanborn Fire Insurance Maps are the perfect place to start. Originally created for assessing fire insurance liability in urban areas, these maps have become invaluable tools for historians, genealogists, preservationists, and anyone interested in the built environment of the past.

What are Sanborn Maps?

First produced in the 1860s by the Sanborn Map Company, these highly detailed, color-coded maps documented the structure and use of buildings in towns and cities across the United States. They include everything from construction material to the number of stories, location of doors and windows, and property boundaries. While their original purpose was to help insurance companies assess risk, today they serve a different function: helping us trace the evolution of our communities.

While the Sanborn Map Company is the most famous producer of fire insurance maps, it wasn’t the only one. In fact, Sanborn’s origins trace back to Daniel Alfred Sanborn, who was originally contracted by Aetna Insurance to produce maps under his own name in the 1860s. These early maps, sometimes referred to as Whipple or D.A. Sanborn maps, laid the groundwork for what would become the Sanborn Map Company in 1867. Around the same time, other firms like Perris & Browne, Hopkins, and Hexamer were also producing detailed fire insurance maps for specific cities or regions, particularly in the Northeast and Mid-Atlantic. Some of these companies were eventually absorbed by Sanborn or phased out as Sanborn became the dominant player. Today, Sanborn maps are the best known because they were produced for so many communities across the United States and because their records have been well preserved and digitized by institutions like the Library of Congress.

Milford, MA Sanborn Map title page.

Where to Find Sanborn Maps

Many libraries, especially those in major cities or with dedicated map divisions, offer access to Sanborn maps. The Library of Congress Geography and Map Division is a standout resource, offering a large digital collection online. Local libraries, historical societies, and town archives are also worth checking.

Library of Congress.

How to Use Them

Using Sanborn maps requires a bit of orientation. Start with the introductory material in each volume, which includes title pages, indexes by street or block, and often a graphic index that shows how each sheet fits into the city grid.

Once you've found your location:

  • Use the key to interpret abbreviations (like “D” for dwelling or “Sal” for saloon), color codes (yellow for frame buildings, red for brick, blue for stone), and line styles (solid for walls, breaks for doors and windows).

  • Zoom in on changes by comparing different years. You can see how buildings evolved—or disappeared—over time.

Sanborn Map key.

Watch Backlog’s Webinar on Sanborn Maps to Explore These Records in Action

Check out our webinar on Sanborn Maps, where we walk through case studies that show how buildings and neighborhoods have changed over time.

Backlog’s Sanborn Maps webinar.

Brittany Fox

Brittany Fox is an archivist, knowledge manager, and librarian in the greater Boston area. She is dedicated to making the past accessible to current learners and future generations.

Brittany started her career in archives as a work-study student in her undergrad archives at Salve Regina University, where she worked for fellow Backlog archivist Genna Duplisea. Falling in love with the profession, she continued her education at Simmons University, earning a Master of Science in Library and Information Science with a concentration in archival management and a Master of Arts in history. Brittany has worked at many different types of institutions, including academic archives at Salve Regina University and the U.S. Naval War College; the Cambridge Historical Commission’s municipal archive; and the Newport Historical Society, a cultural heritage organization. She has also worked at the digital production lab at Northeastern University and Abt Global’s corporate library.

She specializes in records retention plans, knowledge management tools, policy writing, processing collections, and training sessions. For the last four years, Brittany worked in a corporate setting with Abt Global where she fulfilled the research needs of staff and their clients. She is skilled in being a cross-functional asset in corporate matrix structures as well as being an agent of change in knowledge resource structures. Her background in corporate work styles, plus her technical skills in archives, make her work highly skilled, dependable, and polished. Brittany has additional interests in environmental history, film, and preservation practices. She volunteers her time as the Chair of the Membership Committee of the New England Archivists.

As part of the Backlog team, Brittany writes policies and procedures, archives needs assessments, and other reports. As a newer member of the Backlog team, Brittany has recently contributed to Backlog webinars and is excited to continue sharing her knowledge with this community.

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