Editing Sanborn maps (section)

== Insurance underwriting ==

At the outset of the [[fire insurance]] industry, [[Underwriting#Insurance underwriting|underwriters]] visited every property that was under consideration for coverage.<ref name="ristow1968">{{cite journal|last1=Ristow|first1=Walter W.|title=United States Fire Insurance and Underwriters Maps: 1852–1968|journal=The Quarterly Journal of the Library of Congress|date=1968|volume=25|issue=3|pages=194–218|jstor=29781319}}</ref>  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”.<ref name="keister1993"/>

The maps were utilized 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 department]]s, 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.