You could get lost in these maps and data regarding American English dialects for hours. I learned many things, so as the fact that there are 16 vowels (not just a, e, i, o, u and sometimes y), and 24 consonants. I invite you to check this out. 
And the fact that we haven’s pulled things into a homogeneous language, despite all
the years of electronic mass communication demonstrates, I believe, that we are inherently tribal–that we are wired to strive to be like our local tribe and different than those who we perceive to be outsiders.
Years ago, I saw a guest on a talk show who pulled random people out of the audience and guessed where they were from, based on how they pronounced just two or three words that he selected. His indicator words included pairs such as “marry” vs “merry,” and “roof” vs “rough.” He was amazingly accurate, in come cases placing the person within 50 miles of where they lived. In a couple of cases, his guesses were wildly off until the people admitted that they had grown up in the area he had guessed but no longer lived there.
Interesting sidebar: there is a little-known field of science known as forensic linguistics that uses linguistic traits to try to solve crimes. In one case, an expert in this field was able to pinpoint the home city of a criminal on the basis of terminology the criminal had used in a ransom letter, because a distinctive phrase in the letter (“devil strip”) was unique to only one U.S. city (Akron, OH). One of the suspects was from this city, and this person later confessed to the crime.
Check out John McWhorter’s Our Magnificent Bastard Tongue: The Untold History of English.