Someone at Facebook "was interested in seeing how geography and political borders affected where people lived relative to their friends. I wanted a visualization that would show which cities had a lot of friendships between them". The result was this visual (click for huge version):
How cool is that. Immediately I started looking at areas of activity and where they connect to. Then I started to notice the areas without activity and connectivity (Like Russia, China and most of Africa). This would be a great visual to share with students. See what they notice and possibly have a conversation about those dark areas and what that means.
Read more here on Facebook's official blog.