After all, it’s a vast trove of data, tantalizingly accessible; Twitter alone generates about 500 million short messages per day. “Some research starts with, here’s this problem we want to solve, and some starts with, here’s this opportunity, let’s see what we can do with it,” says Dan Tasse, a doctoral candidate in human-computer interaction at Carnegie Mellon who authored a recent conference paper titled “Using Social Media to Understand Cities.” “This was kind of the latter … we saw, ‘Well, shoot, we have pretty detailed information, and it’s just publicly available.”