a blog by Peter Leonard
On June 4-5 I had a chance to go down to the NYPL and participate in their “Mobilizing Historic Geodata” event.
Organized by NYPLLabs, the hackathon brought together programmers, map librarians, and others with an interest in working with historical spatial data.
One of the most interesting parts of the event for me was working alongside some folks who were involved with Flickr in the mid-2000s. Schulyer and Aaron gave some fascinating background on the ways that Flickr was able to take aggregate geolocation data for millions of photographs and create rough outlines of neighborhoods, as defined by people describing their own photos.
We all worked on various projects, ranging from the nearly-complete to some preliminary proofs-of-concept. One thing I threw together on the last day was a tool for finding pre-1921 street addresses in Detroit. That city’s numbering system changed in 1921, which means that all references to house or building numbers before that year do not resolve to their proper location when using tools like Google Maps or OpenStreetMap. Luckily, motivated folks have uploaded information about the change, as well as detailed tables of old and new street numbers drawn from circa-1920 Detroit phone books. The tool I worked on visualizes these changes on a modern street map of Detroit, drawing a red highlight along the path of a street as it existed circa 1921. Markers along the path show where address ranges would have fallen on a block-by-block basis — and also expose former streets that have disappeared since the 1920s, such as the intersection of Abbot and Michigan Avenue, below:
