I disagree about the quality of the information presented herein. As someone whose day job involves recording sound for film (necessarily including lots of dialog) and who is not American, regionalisms in accents are both challenging and fascinating for me, and a frequent topic of discussion between myself and the actors I work with. On smaller films there isn't usually the budget for a dialog coach and since I listen to people for a living that aspect of production often falls in my lap.

I found these maps extremely informative and and they helped to clarify some perplexing edge cases (eg people from Missouri sound southern in general, but on some words they exhibit marked differences from their near neighbors).