How to Read a Sanborn Map

Sanborn Maps are large scale street plans that were created by the Sanborn Map Fire Insurance Company for fire insurance purposes. They provide a wealth of information, such as building outline, size and shape, construction materials, height, building use, windows and doors, street and sidewalk widths, property boundaries, house numbers and more. The plans often include information and shading for steel beams or reinforced walls, plus symbols for stables, garages, warehouses, etc. Factories are labeled with the owner's name, as well as the products manufactured there. In large commercial, public, and factory buildings, even individual rooms and their uses are recorded.

Keep in mind that these maps were intended for use by fire insurance companies. Often, areas of the city not of interest to fire insurance companies weren't mapped. Only built-up parts of cities and towns were surveyed, usually urban areas. While a map showed every building in the area it covered, the focus was on buildings of most importance to fire insurance companies. Dwellings and small commercial buildings would usually just have the basic information provided in street address, building size, building shape, number of stories in the building, roofing material used, and maybe the location of windows. The most detail was given to large commercial, public, and factory buildings. These buildings were the ones that had details on fire hazards inside the building and on the fire protection systems used to protect them. Also, these buildings often had notes written on them, or written elsewhere on the sheet, that went into detail on their building construction and fire protection. Abbreviation were often used do the lack of space. Abbreviation glossaries can be found at  Sanborn Abbreviation Glossary.pdf (duke.edu)  and  Key.PDF (mit.edu) 

Sheet 39 of Vol. 1921-1922 shows an area that has a mix of residential and small commercial buildings. Notice there isn't a lot of detail given about most of the buildings. The exception is the Auto Sales and Service building near the bottom of the page. It has more details about the building than the other buildings on this map. It also has a note next to it about fire protections and extra building construction information.

Sheet 44of Vol. 1921-1922 shows an area consisting of small commercial and large commercial buildings and several factories. You can see that the small commercial buildings don't have has much information about them as the large commercial buildings. The large commercial buildings have the names of their buildings on the map while the small commercial buildings do not and the large commercial buildings also have more detail on them and also have extra notes of their construction and fire prevention. The factories in this area have so much detail and information written inside of them they are hard to read. Note that some of the factories have notes written on the side of the sheet because they can't fit everything inside of the building.

There is a Sanborn Symbols Key on the first page (title page) of every Sanborn Volume. The key to symbols shows the colors and symbols used on the maps in volume. A lot of the symbols are common to most of the editions, but you still want to look at the key to your volume for any differences unique to your volume.

Keep in mind that Sanborn Fire Insurance Maps were created for fire insurance companies, who were familiar with the symbols, and not the general public.

The key contains a lot information crammed into a small space, so it can be difficult to read. I have created a table of these common symbols that I will be using for this guide.

Each Sanborn Map covered a specific area of the city and each map had its own sheet number. The sheet number is the large number at the top left (odd sheet number) or the top right of the page (even sheet number). If this sheet number was different from the previous edition, the previous edition information was in parenthesis below the sheet number.

The large numbers on the outside of the sheet referenced other sheets in the volume. These numbers indicated the area covered by that sheet number.

• This sheet is sheet number 39. The previous edition sheet number for the area covered by sheet 39 in this volume is volume 2 sheet 154

• The number 25 written on the bottom of the sheet below East Broad Street indicates that the area south of East Broad Street between N. Grant St. and N. 9th St. is part of sheet 25.

Each Sanborn Map showed the street information for the area covered by the map. It included street names, street addresses, street width, street elevation, and block numbers.

Street Names were written in large bold print. "Street" was often omitted from a street name and direction names were often abbreviated.

The street address of a building was written outside of the building in the street it was associated with. Large buildings were sometimes associated with multiple street addresses. Multiple buildings on a property often had the same addresses. For example, a dwelling might have an auto garage on its property and both buildings would have the same address.

Street widths were measured in feet and were written in the streets. They were written as a number with an apostrophe next to the number.

If noted, street elevation was indicated with a number in a circle written on a street.

Sanborn Maps were often assigned block numbers. A block number was an official number provided by the city or by the Sanborn Map Company if one wasn't provided by the city. Block numbers were written in large bold print. Block numbers were usually written in a area that divides the block into equal portions. If the block number changed from a previous edition, the number used in the previous edition was written in parenthesis below the block number.

This example is block number 6 from sheet 39. Block 6 is bound on the north by East Gay Street, the east by Cleveland Avenue, the south by East Broad Street and the west by North Grant Avenue. The number 6 is written in an area that divides the block into equal portion.

In the lower left of the this example we see a building with the name OFFICES. Below the building is the number 368. The number is on E. Broad Street. The street address for this building is 368 East Broad Street.

In the lower right corner of this example there is written "60'". This indicates that Cleveland Avenue is 60 feet wide. "66'" written in the lower right corner indicates that North Grant Avenue is 66 feet wide.

A compass was drawn on every Sanborn Map. The compass showed which way was north, east, south, and west on the map. The birdseye view of Sanborn Map didn't always indicate the top of the image as directionally North. The compass on sheet 39 is showing that the area covered isn't true north-south.

Every Sanborn Map had a scale of feet. The vast majority of Sanborn Maps were drawn at a scale of one inch to fifty feet. You can use the scale to measure the size of a building on the map. The shape of each building was also drawn to scale. The scale on sheet 39 is the standard one inch to fifty feet.

Each colored shape on a Sanborn Map represents a building. Every one of these buildings' size and shape is drawn to scale. The area covered in each Sanborn Map included all of the buildings that existed when the map was created. The more important a building was to a fire insurance company (large commercial buildings, public buildings, and factories) the more detail about the building was included by the Sanborn Map surveyor you mapped the area.

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