Music mindmap thing

Music Plasma looks like a really good idea. Type in the name of a band or 'artiste' and you'll see a blobby map of other bands with your chosen one in the middle. The closer the other bands are to your chosen one, the more similar they are (apparently - looks about right to me). The size is meant to denote popularity, but I don't know how they work that out, as it looks wrong to me in places. Maybe it goes on Amazon sales figures? Still very clever though.