Introducing mapsnap: Automated Georeferencing for Historic Sanborn Insurance Maps

Over the past few months I’ve been working on mapsnap, a program to automatically georeference old insurance maps. This post explains why these maps are interesting, how mapsnap works, and why this is 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 the unique view they provide into the history of urban spaces before the major urban renewal projects of the mid-20th century. You can read more about Sanborn maps at the Library of Congress, or watch this six-minute explainer video. Here’s an example of one page from a Sanborn map (NY 1923 vol 1 p27): You can zoom in to see more details:…