Doubtless accurate, even here in the US I grew up in an area that pronounces water “wuhter”, and had to unlearn that when I moved to a city where that would confuse people. That said, I also picked up “y’all” from a friend in college, so it’s a mixed bag.
But when I visit home for a week and come back, definitely some "wuhter"s slip out before I get back into full city mode.
that would be a good map. Especially if you had the IPA on it