Really good question. We started with a list of the 5,000 highest population cities in the U.S and tried to generate maps of as many of them as possible. We are using Open Street Maps data as our source, which is generally pretty amazing but didn't provide the data in the format that we needed it for every city. There were a good couple hundred cities that we wanted to generate but didn't. We hand generated binding boxes for a good number of very large cities, but didn't do it for all of the missing ones.

If you'd like, we can make one for Madison!