Sanborn maps

The Sanborn maps themselves are large-scale lithographed street plans at a scale of 50 feet to one inch (1:600) on sheets of paper. The maps were published in volumes, bound and then updated until the subsequent volume was produced. Larger cities would be covered by multiple volumes of maps. Between editions of published volumes, map updates were sent out as correction slips. Sanborn employees, called "pasters" or "correctors", would visit subscribers' offices to paste the slips on top of the old maps. The map volumes contain an enormous amount of information. They are organized as follows: a decorative title page; an index of streets and addresses; a ‘specials’ index with the names of churches, schools, businesses etc.; and a master index indicating the entirety of the mapped area and the sheet numbers for each large-scale map (usually depicting four to six blocks); and general information such as population, economy and prevailing wind direction. and North Tarrytown describes, in detail, the strength of fire departments in each of the two villages The maps include outlines of each building and outbuilding; the location of windows and doors; street names; street and sidewalk widths; property boundaries; fire walls; natural features (rivers, canals, etc.); railroad corridors; building use (sometimes even particular room uses); house and block number; as well as the composition of building materials including the framing, flooring, and roofing materials; the strength of the local fire department; indications of sprinkler systems; locations of fire hydrants; location of water and gas mains; and even the names of most public buildings, churches and businesses. Unique information includes the location of the homes of prominent individuals, brothels, and more ephemeral buildings including outhouses and stables. == Insurance underwriting ==

At the outset of the fire insurance industry, underwriters visited every property that was under consideration for coverage. As insurance companies increased their service areas, it was no longer practical to send people to every insurable property to assess the risk. The Sanborn maps allowed them to underwrite properties from the office, pooling the cost with other insurance companies that also subscribed to the maps. It was said that at one time, insurance companies and their agents “relied upon them with almost blind faith”. The maps were used by insurance companies to determine the potential risk of a particular building, taking into account all of the information included on the map: building material, proximity to other buildings and fire departments, the location of gas lines, etc. The decision as to how much, if any, insurance would be offered to a customer was often determined solely through the use of a Sanborn map. The maps also allowed insurance companies to visualize their exposure in their coverage areas; when an agent sold a policy, he could color in the corresponding building on the map. == History ==

In the late 18th century, insurance companies in London began to create detailed maps to give underwriters the information they needed to assess fire risk. The practice was adopted by American insurance companies in the mid-19th century. In 1916, Sanborn purchased its last major competitor, the E. Hexamer & Sons of Philadelphia, and became a monopoly. Company headquarters moved to 629 Fifth Avenue in northern Pelham, New York, but there were also regional offices in San Francisco, Chicago, and Atlanta. The Sanborn Company sent out legions of surveyors to map building footprints in all major urbanized areas, along with building details related to fire risk. At its peak in the 1920s, the company employed about 700 people, including about 300 field surveyors and 400 cartographers, printers, managers, salesmen, and support staff. Areas under intensive development were surveyed every six months. Each insured property was listed on a single card, and no map was kept. Corporate mergers also reduced the need for Sanborn Maps, since the consolidated company only needed to buy one set of maps. As insurance companies increased in size, they could withstand larger disasters and no longer needed to use insurance maps to reduce their concentration of risk. Companies also cited "modern building construction, better building fire codes, and improved fire protection methods for the decline in importance of fire insurance maps." With the decline of its insurance business, Sanborn could no longer afford to maintain its army of surveyors. However, the company continued to sell its maps and perform some updates. Government sales began to play a larger role, especially the Census Bureau and municipal planning agencies. Sanborn printed its last catalog in 1950, created its last new map in 1961, and issued its last update in 1977. == Modern uses of fire insurance maps ==

Sanborn maps are found primarily in the archives and special collections of town halls and public and university libraries, and remain a resource for people in many different fields. The maps facilitate historical research through the study of urban growth and decline patterns, and for research into the evolution of specific buildings, sites and districts. Genealogists use the maps to locate the residences and workplaces of ancestors. Planners use the maps to study historic urban planning designs. Historic preservationists use the maps to understand the significance and historical evolution of buildings, including their historic uses and building materials in conservation and rehabilitation efforts. Demographers and urban geographers use them to study patterns of growth and migration of populations. Environmental scientists also use the maps for historical analysis of properties, as the maps often showed the locations of gas stations, drycleaners, and other potential sources of soil and groundwater contamination. Historic Sanborn maps are available through public or university libraries, including the Library of Congress, and from the copyright owners, Environmental Data Resources (EDR), a division of LightBox. ==See also==