Facebook intern Paul Butler has been poring through some of the data held by the social networking firm on its 500m members.

The map above is the result of his attempts to visualise where people live relative to their Facebook friends. Each line connects cities with pairs of friends. The brighter the line, the more friends between those cities.

After tweaking the graphic and data set it produced a "surprisingly detailed map of the world," he said in a blog post.

"Not only were continents visible, certain international borders were apparent as well," he wrote.

"What really struck me, though, was knowing that the lines didn't represent coasts or rivers or political borders, but real human relationships."

However, large chunks of the world are missing, such as China and central Africa, where Facebook has little presence.