The Echo Nest provides a music intelligence platform to hugely popular services like Rdio, Spotify and MTV, so they have a ton of data on what people across America like to listen to. By digging into this well of information they were able to discern what states listen to specific bands more than other states and created a map that displays that data. For more info check out the blog of Paul Lamere, director of developer platform at The Echo Nest, who broke down the data further.
(h/t Business Insider)