everynoise.com does something like that. They don't describe their methodology in detail, but they use some sort of feature extractors to assign positions to g

everynoise.com does something like that. They don't describe their methodology in detail, but they use some sort of feature extractors to assign positions to genres (as some people have define them through song inclusion/exclusion) in a multidimensional space. I believe they use some form of PCA, so the axes aren't so easy to put names on, but it does give some indication of actual variation.