You may have seen earlier this summer a series of maps released by Twitter showing thegeography of different cities as revealed by millions of tweets. Such maps of digital information are compelling for the way they also illustrate concrete infrastructure: the road networks around cities, the public parks inside of them, the clusters of commercial office buildings.
Maps of geo-tagged tweets always represent a biased sample of a biased sample. Tons of people aren't on Twitter. And of those who are, the vast majority never opt in to sharing their geographic location. The 275 million tweets shown in Mislove's map, collected between 2011 and April of the year, reflect just the 1.5 percent of messages that are readily geo-tagged. Still, these people appear to give a pretty impressive snapshot of the transportation networks of large stretches of the globe.