🗺️ How to Read Your Sanborn Map

Decode the past — one color and symbol at a time.

Sanborn Fire Insurance Maps were originally created to help insurance companies assess fire risk in buildings across the United States. But today, they offer something even more fascinating: a window into what your town looked like over 100 years ago.

Reading a Sanborn map is like learning a new language — once you know how to interpret the colors, lines, and abbreviations, you’ll be amazed by what you discover.

🎨 Building Material Colors

Sanborn maps used a consistent color system nationwide to represent different types of construction. Here’s what the colors mean:

  • Red/Pink = Brick or tile buildings
  • Yellow = Wood-frame buildings
  • Olive Green = Fire-resistant materials (like terra cotta)
  • Gray = Adobe, stone, concrete, or iron structures
  • Blue = Concrete or cinder block


See image below: Sanborn Color Key

🛠️ Symbols & Abbreviations

Sanborn maps are packed with shorthand, each packed with meaning. Here are a few of the most common:


  • = Dwelling (residential home)

  • = Store

  • = Flat (apartment)

  • = Saloon

  • = Asbestos Clapboards

  • = Two stories and a basement

  • = Store in basement

Sometimes these are combined — like “2B Sal” — which might tell you that a two-story saloon had a basement, too.

See image below: Sanborn Symbols Key

📐 Map Scale & Sheet Numbers

Most Sanborn maps were drawn at 1 inch = 50 feet, offering incredible detail. Some suburban or industrial maps used different scales — like 1 inch = 100 feet or 200 feet.

Each map is part of a numbered sheet system. Sheet numbers don’t always follow a predictable pattern, especially in large cities, so it’s worth referencing the map’s index or key page to find the sheet that covers your area of interest.

🧭 Key Maps & Indexes

If your town has more than one sheet, there’s usually a Graphic Index or “Key Map” showing which part of the city is on which page. These often include compass roses and color-coded outlines. You’ll also find Street Indexes (alphabetical lists of streets and cross-referenced sheets) and sometimes Special Indexes for businesses, schools, and public buildings — like a historical phone book!  So we advertise the front page or downtown most of the time but if you want your specific street printed we can do that, just send us an e-mail!

🚒 Fire Protection & Water Reports

Many larger towns include a written summary describing the fire department, number of hydrants, water pressure, and even which parts of town were protected by different fire companies. This is pure gold for anyone interested in historical infrastructure or local government.

🗓️ Publication Dates & Updates

Look for a publication year on each map sheet. Some editions include hand-applied correction slips (pasted on by Sanborn employees) showing changes to buildings, streets, or businesses. This helped them keep maps up to date without starting from scratch.

💡 Why It Matters

Understanding these keys helps you turn a beautiful old map into a time-traveling story about your town. You’ll find out where the opera house stood, which block had the cigar factory, or that your great-grandparents lived next to a blacksmith.

At Hometown History Maps, we print these Sanborn gems with all their original detail and color — and now you know exactly how to read them.

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