Sanborn Fire Insurance Maps: 11 Things (2021) You Need to Know

Have you ever heard about Sanborn fire insurance maps?

These maps were originally created to inform fire insurance companies of fire risks in urban areas.

However, they’ve since found a variety of uses, like tracing the subtle change from an agrarian society to a nation of cities and family history.

For more information about how you can continue to use this collection of maps today and where you can find them, keep reading!

1. What are Sanborn maps?

Sanborn maps, also known as Sanborn fire insurance maps, are detailed maps of United States cities and towns created in the 19th and 20th centuries.

They were originally published by The Sanborn Map Company, which is where they derived their name.

The maps were created to allow fire insurance companies to assess their total liability in urbanized areas of the U.S.

Yet, their detailed information about properties and individual buildings in approximately 12,000 U.S. cities and towns has proven useful for documenting changes in the built environment of American cities over many decades.

2. What is the Sanborn Map Company?

The Sanborn Map Company was founded in 1867 by D. A. Sanborn.

It became famous by creating richly detailed fire insurance maps that are full of valuable information and still used today.

Sanborn fire insurance maps were created as a product to help insurance companies assess the potential risks involved in underwriting policies.

They have been developed into a tool with a myriad of uses for multiple industries.

3. What type of information do Sanborn fire insurance maps include?

bulletBuilding addresses

bulletBuilding height

bulletBuilding footprints

bulletStreet names

bulletNumber of stories per building

bulletBuilding construction materials

bulletBuilding use

bulletRight of ways

4. How do you purchase copies of Sanborn fire insurance maps?

If you’re interested in purchasing a copy of Sanborn fire insurance maps, photocopies of documents are usually available for a fee.

You can also find high-quality map reproductions.

For example, the Wisconsin Historical Society provides these for purchase.

Visit here for more information.

5. How do you use Sanborn fire insurance maps for family history?

While Sanborn fire insurance maps are no longer used by insurance agents, they can be used by you for your genealogy research.

Sanborn maps are the closest thing you’ll come to having stop-action aerial photography of your ancestor’s home and surroundings.

With the clues provided on these maps, you’ll be able to learn more and find new documents.

Here’s a summary of how you can use them.

bulletLearn exactly where your ancestor lived

When you find documents related to your ancestors, look for a street name or house number in city directories, WWI or WWII draft registrations, passport applications, etc.

bulletFind maps for that city

Find Sanborn fire insurance map volumes published before, during, and even after your ancestors lived there.

bulletLocate the map sheet with your family’s neighborhood

Using the map index in the front pages of the map volume, locate your family’s neighborhood.

bulletFind the address

Look closely at the individual lot that belonged to your family.

See if you can identify it from the house or lot number.

Look for details like building use, construction, the footprint of buildings on the lot, etc.

Sanborn’s colorful map keys may be helpful as you attempt to deconstruct what you find.

bulletCheck out the neighborhood

What types of buildings or features surround your family’s home?

Are there schools, churches, factories, and other local institutions that may have served your ancestors?

Did your ancestors work at any of these institutions?

How far away were they?

If you know where a relative worked, do you see the workplace nearby?

bulletCompare maps from year to year

The neighborhood where your ancestor lived likely changed from year to year.

Compare maps from year to year so you can see these changes.

Was there new housing built?

What about businesses or roads?

Did street names, numbers, or property use change?

You may also see subtle changes like an outbuilding being constructed or transformed from a stable to a garage.

bulletUse these details to create a description of your family’s everyday surroundings

Using all of these details, you can create your family’s surroundings.

For example, did they live in a brownstone duplex, a frame home, or a tall apartment building?

How close were the neighboring homes?

How large is the lot?

Did they have any outbuildings?

What kinds of buildings or features surrounded the property?

Were amenities necessary for daily life close by or far away?

bulletFind additional records to check

Once you’ve found their area and noted their surroundings, you may see a church, school, funeral home, cemetery, or other institution that may have created records.

This provides another stepping stone where you can find more clues.

Follow up and find more records there next!

6. How are Sanborn maps useful to property owners?

Sanborn maps may be used to research the historical land uses and topography on and around a property.

This can assist with certain aspects of property research, including checking for historic wetlands, flooding or potential environmental contamination.

For this reason, Sanborn maps are often utilized during a Phase  1 Environmental Site Assessment.

7. Were there any other fire insurance map providers?

For much of the 20th century, Sanborn held a monopoly over fire insurance maps.

However, the business declined as U.S. insurance companies stopped using maps for underwriting in the 1960s.

The last Sanborn fire insurance maps were published on microfilm in 1977.

Old Sanborn maps remain useful for historical research into urban geography.

The land data company Environmental Data Resources (EDR) acquired the license for the maps after that, and in 2019, EDR was acquired by LightBox, a real estate services company.

8. What is insurance underwriting?

You may wonder why Sanborn fire insurance maps were used for insurance underwriting to begin with.

Insurance underwriters are professionals who evaluate and analyze the risks involved in insuring people and assets.

They establish pricing for accepted insurable risks.

“Underwriting” means receiving remuneration for the willingness to pay a potential risk.

In the fire insurance industry, underwriters used to visit every property that was under consideration for coverage.

When insurance companies increased their service areas, it was no longer practical to send people to every insurable property to assess the risk.

Sanborn fire insurance maps were used to underwrite properties from the office.

The costs for this were pooled with other insurance companies that also subscripted to the maps.

Insurance companies and their agents trusted Sanborn maps with incredible confidence.

At one point, they were said to rely upon them with “almost blind faith.”

They would use the maps to determine the potential risk of a particular building, including building material, proximity to other buildings and fire departments, the location of gas lines, etc.

Using Sanborn fire insurance maps, the agent would decide how much (if any) insurance to offer the customer.

The insurance companies would also use the maps to help them visualize their exposure in their coverage areas.

If an agent sold a policy, he would color in the corresponding building on the map.

9. Where can I find Sanborn fire insurance maps?

The largest collection of Sanborn fire insurance maps is currently in the Library of Congress, where it has been since 1967.

It includes 1,840 volumes of Sanborn atlases and maps, which serve as the cartographic base for their statical and sampling surveys.

As this is the largest public collection of Sanborn maps available, this is a great place to start!

Depending on where you live, you may also be able to find some collections of Sanborn maps at your public or university libraries as well.

For example, in LA, the Historic Resources Group Collection of Sanborn Fire Insurance atlases is a hard copy collection of 60 volumes covering the city of LA and some local cities in the mid-1950s.

The Historic Resources Group gifted this collection to the Los Angeles Library in June 2004.

The LA Public Library now owns the Sanborn Fire Insurance Atlases in the Library of Congress on Microfilm.

If you’re looking for Sanborn maps in L.A., there are a few steps you must follow.

bulletDetermine the volume covering the requested site or area

bulletCheck the large Sanborn Master Address Index at the desk for the volume number and sheet number for the needed site

bulletCheck the Sanborn guide at the desk under the tabbed pages “Los Angeles” for the appropriate reel containing the volume needed after you’ve found the volume in step 1

bulletKeep in mind that many of the outlying cities are covered by their own Sanborn atlases and are listed in the Sanborn Guide under Cities in L.A. County

bulletWhen in doubt, call the map librarian at (213) 228-7414

While this information is specific to L.A., you may find that a lot of it rings true for your area as well.

You just have to do the research to figure out if there’s a collection of Sanborn fire insurance maps near you and how you can find the one, you’re looking for.

Your local library or university is a great place to start!

10. What are some common myths regarding Sanborn fire insurance maps?

There are a few common myths about Sanborn maps.

Here are false assumptions that you shouldn’t make:

bulletMYTH: Only towns of a certain size were mapped

Both major cities and tiny villages were covered by Sanborn surveyors.

In some cases, small towns were sometimes mapped even more frequently than large cities.

A good example of this is Syracuse, NY.

Syracuse wasn’t mapped at all between 1892 and 1910 while Manlius, a nearby village of only 1,000 people, was mapped four times in the span.

A reason this may have occurred was that mapping a major city was time-consuming and expensive.

Another reason could have been because Sanborn surveys were determined not by population but by demand.

bulletMYTH: Every Sanborn map of an area is similar

Two different repositories may have a 1928 Sanborn map of Brooklyn; however, it’s possible that one atlas may have shown a vacant lot while the other shows a shopping center.

This is due to the economic difficulties in the 1920s.

Sanborn began updating maps by pasting correction slips onto existing maps rather than printing an entirely new map.

Some cities had as many as 50-60 corrections over a few decades.

When this occurred, it often became difficult to tell which slips were added in which years.

Additionally, Sanborn maps and atlases exist in repositories today.

Some were corrected while others were not.

History Associates found that local repositories are particularly likely to have “corrected” versions of the maps.

bulletMYTH: Sanborn maps were only used by the fire insurance industry

Insurance companies were the main consumers of Sanborn maps.

However, city planners, government and municipal agencies, banks, and public utilities also purchased Sanborn maps and atlases as well.

Sanborn also worked with private companies to make specialized maps.

Here are some examples.

In 1952, Business Week reported that Sanborn worked with Safeway Foods to show them where they should expand their stores.

In the early 1940s, the U.S. Census Bureau purchased 1,840 volumes of Sanborn atlases and maps served as the cartographic base for their statistical sampling surveys.

This collection is now in the Library of Congress where it is accessible to the public.

It remains the largest publicly accessible collection of Sanborn maps in the country.

11. How do you read a Sanborn fire insurance map?

Using the following information can help you read a Sanborn map.

bulletLegend

Consult the legend for each individual map.

This is typically found on the first or second page and varies from year to year.

Even if you’ve looked at a Sanborn map previously, don’t assume that you know what this map will look like.

bulletAbbreviation glossary

Check this glossary for a list of abbreviations and obscure terminology that may be found on Sanborn fire insurance maps.

This way, you’ll have an idea of what all the terms used on the map mean.

bulletColor key

This page from the Library of Congress provides information on the different colors used on Sanborn maps and what they indicate.

bulletLine style

Here you’ll find information on the different line styles used on Sanborn maps and what they indicate.

Final thoughts

Previously, Sanborn fire insurance maps were used specifically for insurance underwriting.

Today, they’re used for creative research that can uncover a wealth of information in records that were intended to serve a different purpose.

Whether you’re an ordinary individual looking for information on your family genealogy and history or an experienced historian looking for valuable information from unexpected sources, Sanborn maps can help.

That said, understanding the context of the resource allows you to accurately interpret the information, and we hope this article has provided some of the necessary history behind Sanborn fire insurance maps.

Additional Resources

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Disclaimer: we are not lawyers, accountants or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.

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