Facebook engineering intern Paul Butler put together this nifty map using social graph data. He took a ten million friend pair sample size and created a visual representation of human relationships.
Here's how he did it:
I defined weights for each pair of cities as a function of the Euclidean distance between them and the number of friends between them. Then I plotted lines between the pairs by weight, so that pairs of cities with the most friendships between them were drawn on top of the others. I used a color ramp from black to blue to white, with each line's color depending on its weight. I also transformed some of the lines to wrap around the image, rather than spanning more than halfway around the world.
Via Tech Crunch