AN INTRODUCTION TO FIRE INSURANCE MAPS 

IN THE LIBRARY OF CONGRESS

by Walter W. Ristow

During the past century the Sanborn Map Company has published maps and atlases of more than twelve thousand United States towns and cities, issued in some seven hundred thousand separate sheets, and yet the name Sanborn is known to but a small number of American map users. This anomalous situation has persisted because Sanborn’s specialized maps were prepared for the exclusive use of fire insurance companies and underwriters.

Insurance maps and plans originated in London toward the end of the eighteenth century in response to the need felt by large fire insurance companies and underwriters for accurate, current, and detailed information about the buildings they were insuring. Although a fire insurance company was established in Philadelphia as early as 1752, the number of domestic companies was quite limited before the War of 1812. Both before and immediately after the Revolution, London fire underwriters wrote most of the fire insurance for buildings in American cities. Animosity toward the British grew more intense during the War of 1812, and this feeling plus restrictions on foreign companies operating in the United States encouraged existing American companies to expand their activities and stimulated the formation of new companies. New York, Philadelphia, Boston, and Hartford became the principal fire insurance centers.

In 1835 a major conflagration in New York City caused losses of more than 20 million dollars and wiped out most of the nation’s smaller insurance companies, which had little or no reserve funds. In the reorganization of the industry larger companies were formed, and states and cities passed laws requiring reserve funds and issued other regulations. Personal inspection of properties under consideration for insurance became impossible and a demand for maps giving essential risk information developed.

George T. Hope is generally credited with having fostered the idea of specialized and detailed fire insurance maps in the United States. Around 1850 Hope, who was at the time secretary of the Jefferson Insurance Company, began to compile a large-scale map of a portion of New York City for use in calculating fire risks. He engaged William Perris, an engineer trained in England, to make the surveys. To ensure that the proposed map would include all essential information, Hope formed a committee of fire insurance officials to direct the project. They agreed that the map should identify the construction materials in all buildings by a system of colors, formulated a set of appropriate cartographic symbols, and agreed on a format and scale for the map. The standards adopted by the Hope committee were followed, with few modifications, for a century or more.

D.A. Sanborn, a young surveyor from Somerville, Massachusetts, was engaged in 1866 by the Aetna Insurance Company to prepare insurance maps for several cities in Tennessee. Before working for Aetna, Sanborn conducted surveys and compiled an atlas of Boston, which included twenty-nine large plates showing sections of Boston at the scale of 50 feet to an inch. The success of the Boston atlas and the Aetna commission must have impressed the young surveyor with the importance of detailed and specialized maps for the fire insurance industry. Following his commission in Tennessee, he established the D.A. Sanborn National Insurance Diagram Bureau in New York City in 1867. From this modest beginning grew the specialized company that has compiled and published maps for the fire insurance industry for more than a hundred years.

D.A. Sanborn died in 1883. The company he founded, however, continued to grow. In 1899 it acquired the Perris and Browne firm. The firm name established by Sanborn in 1867 was changed in 1876 when the firm was incorporated under the Sanborn Map and Publishing Company, which then became the Sanborn Perris Map Company, Ltd., until, in 1902, the name was shortened to the Sanborn Map Company, the form which the company uses today.

Sanborn appears to have begun systematic registering of maps, with deposit copies, in 1883. With the exception of the Boston atlas, the 1868 map of Toledo, and the 1879 map of Rutland, Vermont, the sheets carrying the 1883 date are the earliest in the Library of Congress. Within the next few years deposit sheets were received for cities in virtually every state, suggesting that the years immediately before and following incorporation in 1876 Sanborn had expanded its insurance map coverage to all parts of the United States. Although some of the growth resulted from absorption of other map companies, most of the expansion must be attributed to good managerial procedures and practices. The Sanborn company successfully produced detailed, comprehensive, and up-to-date maps which met the needs of the fire insurance industry.

Sanborn surveyors were at work in all the states, and during the years of maximum production there were as many as three hundred employees in the field and more than four hundred in the main office and publishing plant in Pelham, New York, and in secondary production centers in Chicago and San Francisco. Unfortunately, Sanborn mapmakers worked anonymously, and their names never appeared on the maps they produced.

To ensure uniform standards of accuracy and presentation on its maps, the Sanborn Company published, in 1905, a Surveyors’ Manual for the Exclusive Use and Guidance of Employees. The introduction to the manual emphasized that "Sanborn maps are vastly different from other publications, and the novice must start in with the idea that it is all new, though some former occupation, such as civil engineering and architectural work, should fit a man to readily grasp the primary principles. Our maps," the introduction explained, "are made for the purpose of showing at a glance the character of the fire insurance risks of all buildings. Our customers depend on the accuracy of our publications, and rely upon the information supplied, incurring large financial risks without making personal examinations of the properties." The manual included more than a hundred pages of precise instructions and included sample maps and a comprehensive symbol key.

"The information reported," the Sanborn surveyor was advised,"is technical to the fire insurance world, and you should master the technicalities and ever bear in mind the use to which the map you are producing will be applied."

Maps were drawn at a scale of 50 feet to an inch, on sheets 21 by 25 inches, which were cross ruled in one-inch squares. The manual instructed surveyors to map all the built-up part of the town or city. "Information," they were told, "is generally available at the Court House, or...some real estate agent may have the necessary data. [However] if records are not easily obtainable do not waste too much time, but proceed to measure up the territory with tapeline, and plot sheets from notes so secured. In plotting put on the street names and widths and real estate description."

Each year Sanborn extended its coverage to additional cities and also issued revised editions and paste-on correction slips for previously published maps and atlases. Production probably reached a peak in the early 1930s. An article about the Sanborn Company published in the February 1937 issue of Fortune Magazine stated that "Sanborn maps describe the houses on every street in more than 13,000 U.S. towns and cities...[and] cost anywhere from $12 to $200 [per map] depending on the technical difficulties involved in making them up."

Sanborn maps were lithographically printed in the company’s Pelham, New York, plant. With the aid of waxed paper stencils, Sanborn employees colored the maps by hand, because there were usually fewer than twenty orders for a single map sheet. They were issued as unbound sheets for towns and cities with maps of under a hundred sheets. Bound volumes, each with approximately one hundred plates, were published for large cities. Thirty-nine volumes were required for New York City. Around 1920 the company introduced a loose-leaf atlas format which made it possible to replace outdated plates without reprinting an entire volume.

Sanborn early learned that having a monopoly in a very restricted and homogeneous market invited critical observation and evaluation. Most of the company’s customers were members of national or regional underwriting associations where they could discuss Sanborn’s real or assumed deficiencies. One of the major concerns was the relatively high cost of Sanborn’s products and services.

The fortunes of the Sanborn Company did not depend, however, solely upon their relations with fire insurance underwriters. Economic, political, and social conditions also influenced the sale of Sanborn maps and services. Thus, the construction boom in the middle and late twenties had an accelerating effect on fire insurance sales and upon the need for maps. During these years Sanborn prepared maps of a number of new towns and cities and resurveyed previously mapped areas. For particularly active construction areas, revisions of Sanborn maps were issued at six-month intervals.

The period of economic prosperity did not last and with the financial crisis of 1929 and the depression of the thirties, construction was curtailed, fire insurance sales lagged, and companies again exerted pressure on Sanborn to reduce the cost of its maps and services. Sanborn’s response was to offer cash discounts to subscribers, offer the paste-on service for sheet maps (i.e., those for smaller towns and cities), and to mount the sheet maps on cloth to ensure longer life.

World War II placed mandatory restrictions on construction and on the publication of maps. Sanborn, like most other map publishers, survived during these years by producing maps on contract for the military services. The hoped-for postwar prosperity was slow in arriving, particularly for the Sanborn Company. In an attempt to bolster declining sales, maps were published for a number of cities at reduced scales of one inch to 100 feet and one inch to 200 feet (as compared with the standard one inch to 550 feet) and issued in small-size atlas format.

By 1960 it was apparent that the fire insurance industry was undergoing major changes and the detailed maps and services offered by Sanborn were no longer required. In its 1961 report the National Bureau of Fire Underwriter’s Map Committee noted that some companies had discontinued the use of maps and decided "to review the overall situation from the stand-point of the needs of the business at the present time."

Although Sanborn maps today have minimal interest for the fire insurance industry, the Sanborn Company is supplying updated copies of many of its maps and atlases to various clients. Today municipal governments are Sanborn’s best customers, accounting for 60 percent of map sales and services. Engineering and architectural concerns are also significant purchasers of corrected Sanborn maps.

The large file of non-current Sanborn maps and atlases constitutes an invaluable historical record of urban growth in the United States over more than a century. Local historians, genealogists, urban planners, geographers, economists, and other specialists and scholars consult the maps today for the wealth of detailed data which they embrace. The largest collection of Sanborn maps and atlases is preserved in the Geography and Map Division, Library of Congress, where there are an estimated 700,000 Sanborn maps in bound and unbound editions.