I just checked /r/truereddit to see what it had, they also had a bigger version of the map: https://pbs.twimg.com/media/BDoqLqeCQAA0Jbq.jpg:large What struck me then is if you look at the bottom left they have the source. They only pulled the top 100 most recent posts, which seems like a bad idea. This would be incredibly susceptible to the timing then, especially in major cities where a lot of posts might happen. Pulling the most recent 100 posts in NYC on a Monday morning would probably give you only posts from the weekend and then likely to be Bars/Clubs, if you pulled that instead on a Thursday morning you are more likely I'd bet to get Subway. Also, craigslist is broken up by cities, so this isn't really representative of a state as a whole potentially. I guess my point, this isn't really very good academic work.
Oh, good point inre: source. I thought the same, although I didn't bother to do any research, which is why I passed on sharing it. I also didn't really think it was up to truereddit standards, but that doesn't really matter. Still entertaining to look at.