- fireproofed or construction of non-combustible materials is indicated by brown. Wall thickness, the number of window openings on each floor, and building dimensions including height are all documented. Building use is recorded, often very simply such as “D” for dwelling or “A” for private automobile garage. Commercial buildings are detailed with type of business, sometimes with specific firm names for larger structures. If a business used a heat source in part of its process, kilns, smelting furnaces, and smokehouses are all typical examples, the specific location is indicated on the map as are any concentrations of flammable materials.
- stone or masonry construction is blue
- solid brick construction is red
- Because of the depth of historical land use data, corporations and individuals interested in acquiring a particular piece of property often use fire insurance maps to determine if there is a possibility of needing to invest in environmental remediation. Urban history studies can be enhanced by using fire insurance maps to track how particular plats of land or buildings were used, to establish a sequence of construction, demolition and new construction, and to trace industrial growth. Family historians have used fire insurance maps to confirm details in family letters about places of both residence and employment and about transportation methods, foot, streetcar or urban rail lines, between home and work. Fire insurance maps of urban areas originally were produced to assist underwriters in determining the chances of a specific building being destroyed by fire based on its construction, heat source, use, and the neighboring structures. At first, small companies insured urban construction in their immediate vicinity. But eventually small providers were aggregated to create larger companies, and centers of the insurance industry quickly developed in Hartford, Connecticut, Boston, and New York. Large companies, or companies that insured structures scattered through a large area, were no longer able to do field surveys of the buildings they had contracted to insure. Fire insurance maps became a proxy for personal visits. The Aetna Fire Insurance Company was an early and enthusiastic adopter of fire insurance maps. In 1866, Aetna hired David A. Sanborn to prepare maps of cities in Tennessee. The Sanborn Map Company became the overwhelming leader in preparing fire insurance maps and had a near monopoly by 1920. Construction methods are shown on fire insurance maps by color: wood frame construction is yellow