A new study (lots of math, only one map) by researchers within the Social Cognitive Network Academic Research Center (SCNARC) at Rensselaer Polytechnic Institute drew on data from Gowalla. It finds that despite connections to individuals far and wide, people are most likely to have friends that are local and be influenced by those locals. Taking people at random at the same location, at a concert say, does not make them more likely to be friends. A key stat: 80% of people's friends live within 600 miles of them. 

- Brafton

In somewhat related news, the New York Times addresses why it's so hard to make "real" friends after 30. The answer? Frankly, geography:

As external conditions change, it becomes tougher to meet the three conditions that sociologists since the 1950s have considered crucial to making close friends: proximity; repeated, unplanned interactions; and a setting that encourages people to let their guard down and confide in each other, said Rebecca G. Adams, a professor of sociology and gerontology at the University of North Carolina at Greensboro. This is why so many people meet their lifelong friends in college, she added.

- NY Times