The geography of popular music has changed considerably over the past couple of decades. The internet and social media have obviously played a large role. While industries like automobiles or steel still cluster around resources, cheap labor and transportation routes, or high-tech companies cluster around skilled labor and universities, the forever altered music industry now has fewer physical reasons to cluster — musicians no longer need to be near any particular resource to record and distribute their work anymore. And yet, they clearly still do cluster, just perhaps for slightly different reasons. (I've written about the role of place in music before as well as here, here, here, and here).
Most previous studies of music, including my own, have relied on data from government sources (like the U.S. Census Bureau, the Bureau of Economic Analysis, and the Bureau of Labor Statistics) which are limited essentially to counting the number of musicians or music-related firms. But over the past decade or so, new data have become available from social media sites which can provide a wider range of information on the popularity of musical acts and the genres they play.