I think this visualization could be nicely completed by community labels. To go on with the city metaphor, you could have a road sign for each cluster of buildings. I can count 10 big community in the StackOverflow metropolitan area. A modularity algorithm would identify these clusters. Then you could get a list of most frequent tags in the users of the cluster to build the road sign.
When speculation has done its worst, two plus two still equals four. -- S. Johnson