Reading a Sanborn map: a field guide

Between 1867 and 1977, the Sanborn Map Company drew nearly every commercial block in America at a scale where individual buildings have shapes, materials, and labels. They did it so fire insurers could price risk. What they accidentally built is the most complete record of American small-town life that exists.

Pink means brick, yellow means wood, and the little circles are cisterns. Once you can read the code, a 1901 sheet tells you which block was thriving, which hotel had actual plumbing, and where the livery stood before it became a Chevron.