Historic maps · Land records · October 6, 2026
Sanborn Maps: What They Show and How to Find Them
Sanborn maps are detailed fire insurance maps of U.S. towns from 1867 on. See what they show, how to read the colors, and where to view them free.
Sanborn maps are large, hand-colored maps that show American cities and towns building by building, made so fire insurance companies could judge the risk of a property without sending someone to look at it. The Sanborn Map Company and its founder, surveyor D. A. Sanborn, began publishing them with an 1867 atlas of Boston, and the series went on to cover roughly twelve thousand communities in the United States, Canada, and Mexico. For anyone researching an old house, a former business, or how a block looked a century ago, they are one of the most detailed records available, and many sheets can be viewed online for free.
What Sanborn maps show
Each sheet covers a few blocks at a large scale, often 50 feet to the inch, which is big enough to draw the outline of every building. Because the maps were made for insurers, they record the details that affect how a fire starts and spreads:
- Building footprints, including porches, sheds, and rear additions.
- Construction material, shown by color, plus the number of stories and the type of roof.
- Building use, such as a dwelling, store, church, stable, or factory, often with the business named.
- Fire protection features, including fire walls, sprinkler systems, water mains with their sizes, hydrants, and alarm boxes.
- Streets and addresses, with street names and widths, house numbers, and block numbers.
- Lot lines, drawn to show how the land was divided at the time.
How to read the colors and symbols
Start with the key, which is often near the front of a volume. Colors carry most of the information. In the standard Sanborn scheme, reddish pink marks brick or tile, yellow marks wood frame, blue marks concrete or cinder block, olive green marks fire-resistant construction, and gray is used for adobe and for metal. A number inside a footprint usually gives the height in stories, and letters stand for the use, such as D for a dwelling. Symbols and abbreviations changed somewhat over the decades, so check the key that came with the edition you are reading.
Larger cities were split across several volumes and many sheets. The index sheet, sometimes called the key map, shows which sheet covers which blocks, so look there first instead of paging through the whole atlas.
Dates, editions, and paste-overs
Sanborn did not redraw a town every year. Instead, the company issued new editions every so often and sent subscribers correction slips to paste over the parts that had changed. A single sheet can therefore show changes from different years, and the date on a volume’s title page may not tell you exactly when a given building was drawn. When you need to date something, compare two or more editions. A building that appears on one edition and not on an earlier one was likely built in between.
Where to find Sanborn maps
- The Library of Congress. Its Geography and Map Division holds one of the largest Sanborn collections anywhere and has put a large and growing set of sheets online. You can browse the online Sanborn collection by state and city and zoom in on each sheet.
- State libraries, universities, and historical societies. Many hold paper copies or microfilm for their own state, and some have scanned them. A local reference librarian can tell you what exists for your town.
- Library database subscriptions. Some public and university libraries offer a digital Sanborn database to card holders, often usable from home.
Later editions may still be under copyright, and libraries cannot always copy those for you. Check the rights statement on each item before you reuse an image.
What people use them for
- House history. Comparing editions narrows down when a house was built, when it gained a porch or wing, and whether a garage replaced a stable.
- Old addresses. Many towns renumbered their streets. A Sanborn map can show which old house number matches a building standing today, which helps when old deeds or city directories use the earlier number.
- Former land uses. Environmental reviews before a property sale often look at historical fire insurance maps for signs of old gas stations, dry cleaners, fuel tanks, or factories on or near a site.
- Family history. Paired with census records and city directories, the maps show the house, shop, or block where an ancestor lived or worked.
Sanborn maps vs plat maps and parcel GIS
A Sanborn map is an insurance document, not a survey and not a record of ownership. Its lot lines were drawn to help locate buildings and are not a legal boundary. A plat map is the recorded drawing that created lots in a subdivision, and the current county parcel layer is a modern locating tool built from deeds, plats, and surveys. Our guide to how old plats differ from current GIS explains why old and new lines rarely match exactly, and plat map vs parcel map sorts out the two current record types.
Sanborn coverage also has gaps. The company mapped towns and cities, so open farmland and many rural areas were never drawn. For rural land, the older county plat book or atlas is usually the better historic source, since it shows farm tracts and owners’ names by township.
Compare an old sheet with today’s parcel map
To line up a Sanborn sheet with the present, find the same block on the county parcel viewer from our county GIS map directory. Match the street corners first, since streets move less than lot lines, then count lots along the block. If you are tracing ownership rather than buildings, the deed records are the source to follow; how to do a title search and chain of title explain how.
Sanborn maps FAQ
What are Sanborn maps used for?
They were made to help fire insurers judge risk. Today people use them to date old buildings, find former house numbers, check past land uses during environmental reviews, and research family history.
Are Sanborn maps free to view?
Many are. The Library of Congress has put a large set of Sanborn sheets online at no cost, and some state libraries and universities offer their own scans. Other collections are available through library subscriptions.
What do the colors on a Sanborn map mean?
In the standard key, reddish pink is brick or tile, yellow is wood frame, blue is concrete or cinder block, olive green is fire-resistant construction, and gray is adobe or metal. Always check the key for your edition.
Do Sanborn maps show property lines?
They show lot lines as they were drawn at the time, but they are insurance maps, not surveys. Use recorded deeds, plats, and a survey for legal boundaries.
Does every town have a Sanborn map?
No. Sanborn mapped about twelve thousand cities and towns, mostly built-up areas, and coverage years vary by place. Many rural areas were never mapped, so county plat books are often the better historic source there.