Jason Hong sends me to his project: Livehoods:
About the Livehoods Project The Livehoods Project presents a new methodology for studying the dynamics, structure, and character of a city on a large scale using social media and machine learning. Using data such as tweets and check-ins, we are able to discover the hidden structures of the city with machine learning. Our techniques reveal a snap-shot of the dynamic areas the comprise the city, which we call Livehoods.
Livehoods allow us to investigate and explore how people actually use the city, simultaneosly shedding light onto the factors that come together to shape the urban landscape and the social texture of city life, including municipal borders, demographics, economic development, resources, geography, and planning. Livehoods is a research project from the School of Computer Science at Carnegie Mellon University.
Cool maps at the site.