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.
Facebook intern Paul Butler was interested in the locations of friendships, so he decided to create a visualization of Facebook connections around the globe. How local are our friends? Where are the highest concentration of friendships? How do political and geological boundaries affect them?
Butler started by using a sample of 10 million friend pairs, correlated them with their current cities and then mapped that data using the longitude and latitude of each city. See the pic below:
That was the easy part. Creating the right effect to show connecting relationships between thousands of cities proved to be a challenge. Butler wrote a fascinating Facebook note explaining some of the challenges he faced creating his visualization.