http://internet-map.net/To put it in a short way, this map shows visits and links between sites. The larger the circle, the more traffic it receives. Depending on where the user goes from there, it will form "bonds" between other sites and the circles will be closer to each other. If people keep doing the same thing, the circles will move towards each other. A full, better explanation can be seen by slapping that "about" button up top.
This thing is actually pretty loving cool. It looks like a starmap.