Over the past few months I’ve been working on mapsnap, a program to automatically georeference old insurance maps. This post explains how it works, and why it’s worth doing. I’m interested in history, cities, and maps, and in the United States that combination leads you very quickly to the Sanborn Insurance Maps. The Sanborn Map Company produced hundreds of thousands of detailed, block-by-block maps of every city in the United States from roughly 1870-1960. Their original goal was to help insurance assessment (Is this building made of brick or wood? Where are the water mains?) but today they’re valued for...