Paul Butler analyzed the relationships of cities around the world through the eyes of Facebook.
Visualizing data is like photography. Instead of starting with a blank canvas, you manipulate the lens used to present the data from a certain angle.
When the data is the social graph of 500 million people, there are a lot of lenses through which you can view it. Therefore Paul used a subset of the complete social graph of about ten million pairs of friends. Using the user’s current location, he plotted lines between the cities. The weight of the lines is defined by the amount of connections between the cities. The result is a world map based purely on the connections on Facebook. The shape of the continents and even international borders become visible where Facebook has a large enough user base.
Read more about the process behind the visualization on the Facebook Engineering Blog.