Historic Preservation

Using Sanborn Maps to Research Old Buildings

In the course of researching an old building, the researcher can naturally aid efforts by the use of maps. Information obtained from tax records, abstracts and city directories can be coordinated with maps to place a building within its natural context. The makers of city directories often provided maps with their printed listings; local governments also frequently offered illustrative maps of their own city or town. One type of map, however, is particularly valuable to re-searchers, for it offers not only context but additional information that is unlikely to be available elsewhere. This is the Sanborn map, and, if properly used, it can yield an extraordinary amount of information about a building's construction and uses, as well as the neighbor-hood that the building has been part of during its lifetime.

Sanborn maps were originally used exclusively for the purpose of fire insurance. Mapping for fire insurance began in England around the beginning of the 19th century, and the idea of detailed fire insurance maps spread slowly to America. In 1867, a surveyor named D.A. Sanborn established the Sanborn Map Company in New York City. The Sanborn Company developed a system for standardizing maps that proved so successful that by the end of the 19th century the company was virtually the only fire insurance mapmaker in the nation. Today, the fire insurance aspect of old Sanborn maps is much less important than their value as research tools, and it is for their research potential that thousands of Sanborn maps of hundreds of American cities and towns have been gathered in libraries and archives. Unfortunately, Sanborn did almost no mapping of rural areas.

Scaled drawing that contains
symbols that indicate the
building's size, use and structural
composition features.
Scale: 1" = 50 ft.

Sanborn's system utilized standard symbols and colors designed to, in the words of a company manual, "show at a glance the character of any building." Each building represented on a Sanborn map was drawn to accurately show its true shape and composition. Drawings were scaled so that one inch would equal 50 or 100 feet of actual length, and every set of maps for a particular city or town contained a key to the symbols used to denote structural materials and features. Many Sanborn symbols dealt with the arrangement of fire hydrants and alarms, which would be of limited value to the general re-searcher, but other symbols can be studied for valuable information.

In Figure 1, for example, the scaled drawing contains symbols that indicate the building's size, use and structural composition features, which can readily be understood by looking at the key (an abbreviated version of the key on a set of Sanborn maps). On a regular map, this structure would be tinted yellow to indicate it is a frame construction, while the large "D" reveals the building to be a dwelling or residence. Similarly, the "2B" indicates that the house has two stories and a basement, while the small "x" represents a roof covered by wood shingles. Obviously, frame construction and wooden shingles would be of interest to a fire insurance company, but it might also be of use to the researcher. If this particular Sanborn map was issued soon after the house's construction, it is conceivable that this drawing shows the house as it originally was, before the alterations and additions that are almost inevitable for an old residence. Other drawings on the same map can be studied to learn about the neighborhood, and thus place the old house into a context that probably would not be gained from a city directory or even from tax records.

Drawing that represents a
commercial building, which
at the time the
Sanborn map was drawn
contained three shops.
Scale: 1" = 50 ft.

To take another example, consider Figure 3. This drawing represents a commercial building, which at the time the Sanborn map was drawn contained three shops. Since the Sanborn Company's policy was not to denote commercial uses with symbols but instead to simply write out the uses on the drawing, the illustration shows that the building at this time contains a dry good store, a bookseller and a restaurant ("Rest"). On the actual map this drawing was tinted red to indicate that the building was constructed of brick. The "3" points out that the structure is three stories tall, while along the walls on each side are three "8s" to note that the outside walls on each floor are eight inches thick. As commercial buildings tended to be quite varied, the Sanborn mapmakers did not develop symbols for every possibility, and simply made use of the space inside the drawing to write out remarks. Thus, the ground floor of the structure in this illustration is concrete and the second and third floors are wood. Also, the second and third floors were at the time being used for rooms, or apartments. Finally, the black dot indicates that the building is covered with a composition roof.

For simplicity's sake, only some of the many standard Sanborn symbols have been used in the illustrations; other symbols concerned with the arrangement of windows, the presence of porches or skylights and other information would also be of value to a researcher. Each collection of Sanborn maps for a specific locality was issued with a complete key that once studied would enable a person to decipher each drawing. By the same token, single illustrations from single maps only begin to point out the uses of the Sanborn drawings. In one southern Wisconsin city, for example, seven sets of Sanborn maps were drawn over a forty year period covering the last part of the nineteenth and early twentieth centuries. Since this city issued very few city directories during the same period, the Sanborn maps together with tax records became the principal research tools for studying the growth of the downtown area. The maps served quite well: by comparing the different sets of maps, a researcher could tell when brick structures began to replace frame shops, when specialty stores appeared and general stores declined, and when the commercial area started to expand in what had previously been a residential area. The information gleaned from this method of using the maps aided in the identification of a historic district. Outside Wisconsin, urban historians are using Sanborn maps as regular sources for the study of urban growth and change in major American cities.

Anyone in Wisconsin who is interested in using Sanborn maps to research an old building should know that the Wisconsin Historical Society has a collection of hundreds of Sanborn maps representing a large number of Wisconsin cities and towns. This collection is maintained at the Society's Archives Division in Madison. The collection includes guides to the use of the maps, as well as a listing of the maps that are available. The Archives Division is open during normal business hours, Monday through Friday.