Social Connectedness Index

NYU Stern Associate Professor of Finance, Johannes Stroebel and NYU Stern Assistant Professor of Finance, Theresa Kuchler have ongoing research with Facebook to study the role of social networks in economic and financial decision making.
As part of this research, thry have produced a new data set called the "Social Connectedness Index" -- the SCI -- that is based on data from Facebook, and that measures the connectedness across U.S. counties, and between U.S. counties and foreign countries. 

The data is described in detail in their new paper "Measuring Social Connectedness"