Hi, friends. Here the professor of linguistics talks about the dialects in North America. You can also listen to it with subtitles.
This reminds me of a semi-popular quiz that I took that turned out to be very accurate (state and region) about where I live. o.O
Nonetheless, I still think that with the advent of the Internet, Youtube, social media, and transportation, accents will only neutralize, especially in metropolitan cities like New York or Boston (like when students from around the US go to a specific college and settle there, mixing different accents). In my high school I have teachers from Chicago, Philadelphia, etc. and they hardly sound any different. 
And most of these accent shifts are so slight and minuscule that I feel like these linguists are doing treasure hunting in searching for the slightest vowel shifts 