Nearly 3 percent of the entire population of the world is on Twitter, and those folks have sent about 170 billion messages of up to 140 characters since the service started seven years ago. But it’s only recently that researchers figured out where in real space, not cyberspace, those tweeters were doing all that tweeting. The question is of more than academic importance. As Kalev Leetaru and his University of Illinois colleagues note in the peer-reviewed Web journal First Monday, Twitter messages are increasingly important for monitoring natural disasters; there is even a United Nations crisis map based on data collected from social media. Helped by supercomputers generating “the global Twitter heartbeat,” the Illinois team was also able to get a detailed sense of obsessions and emotions at any given moment. It turns out the average distance between people mentioning or retweeting each other’s messages is 750 miles. A comparison with mainstream media coverage, meanwhile, suggests that the news Twitter provides is less evenly distributed around the globe. Twitter is stronger in Latin America. Mainstream is stronger in Africa. And mainstream is a whole lot stronger in Iran and China. But, of course, Twitter is banned in those countries.