Here's an interesting filter to apply to this map: all of the innovative music from the last 100 years originated in the triangle between Memphis, New Orleans and Nashville—blues, jazz, R&B, rock and roll, and country. All of those genres were born in that small geographical area. It's the Silicon valley of modern music. You could also argue that hip hop is a permutation of blues/r&b.

It's a race thing - most of the country's African American population lives in the south, with little pockets scattered elsewhere. NYT did a similar set of maps for TV shows and the results were similar. White America likes hip-hop, as you can see from the maps but there's almost no interest in other pop music from the south.