Low key writing this has made me realize how much of my life has just been migrating up and down I-40.
I can't speak on Knoxville because I've only spent a day there, but I've spent a good bit of time around Amarillo mostly from driving between CO and TX over a hundred times, although not really in the suburbs.
Saw a lot of beat up trucks that looked like they were owned by blue collar folks and used for truck things. But of course there's also plenty of brodozers, which I'm assuming are also fairly common in Knoxville.
I was just saying two middle class families living a thousand miles away from each other along I-40 were fairly similar to me. They are also considered in the same nation according to this map.
The only part of this map I'd quibble with based on personal experience is Birmingham, AL (and Jefferson County) is definitely in that same Greater Appalachia nation because I can't in my heart of hearts say it and Dothan, AL have anything in common. The most interesting thing in Dothan is a hardware store.
Illinois is an interesting place as it features large changes in culture from north to south. I was born in Northern Illinois and lived there until I was 10 when I moved 5 hours south. There is an enormous cultural difference. As the map shows Northern Illinois is part of the "Midlands" with a flat/generic accent whereas the Southern Illinois/Southern Indiana accent sounds a lot like Woody Harrelson's (who was born in Texas). The greater Chicagoland area is its own thing, the map shows it part of Yankeedom but I disagree - I lived in Chicago twice in my 20s and I've lived in Yankeedom (Massachusetts) for 25 years now and I don't see much similarity. I'd group far northern Illinois, Wisconsin, Michigan and Minnesota in their own group, maybe called the "Opers"
But IMO that's a very far cry from eastern/south-eastern Kentucky, eastern Tennessee, western NC, WV, etc; truly core Appalachia.
Its also a far cry from mid-Indiana, which is culturally identical to northern Indiana, most of Illinois, Iowa, southern Michigan, maybe even as far as southern Wisconsin, Kansas, and Nebraska. That's Corn/Rust belt, very crop-farm oriented, dairy farms, extremely flat, but not as rural as many people think, not nearly as rural as Appalachia or the west.
Culturally, they both share a concern over Gun control for one. Those specific groups happen to align politically on the issue, which is incidental.
They're obviously not related by immigration group either. The Hopi descend from early first nations. The Navajo descend from the athabascan migrations. Yukon comes from Canadian and British gold rush populations. Alberta comes from various prairie settler efforts, including Ukrainian Canadians. The Mormons were their own settlement group in Mexico that went to war with many of the (now-) surrounding indigenous nations. Etc.
And this is just one "American nation". The same basic issue exists in all of them.
The fact there are political differences by region is not a defining factor, or the regions would look very different. The fact it is a cultural topic at all, looks to be one common factor. I feel like I'm talking in circles now.
Regardless, I really don't understand this sort of hair splitting. My imagination isn't that expansive, yet I can understand how these regions might have been determined in many cases. Asking the authors might get answers to these kinds of questions.
Early in the revolution, it was taken by the colonists who declared it “Illinois County, Virginia” and allowed people to stream in and claim their homesteads (Note that the northern part was claimed by Connecticut as their own “Western Reserve”). Essentially all of southern Ohio, Indiana and Illinois was settled by people crossing the river from Kentucky, so it makes a lot of sense that you’d think that the southern parts of all these states seem more similar to each other than they are to their northern neighbors.
The next section north seems to have been mostly dominated by folks from the mid-Atlantic - Virginia, etc. And further north dominated by people that arrived on sailing ships, especially from New York. New Buffalo Michigan refers to Buffalo New York ;)
Anyway, it seems kind of weird that these states seem geographically oriented north-south but culturally oriented east-west. But the fact that they were depopulated (of Europeans) and then repopulated (by Europeans) gives an explanation of that, especially with the transportation available at the time of repopulation (of Europeans).
But southern Indiana is very different. Definitely more similar to Kentucky & Cincinatti-area southern Ohio. You start to get "twangs" of Southern Americana as you approach the Ohio River Valley, which are basically non-existent in northern Indiana. Something about the air is different.
The biggest cultural shock people not from the midwest, and even people from the midwest, often experience about the area is IME northern mainland/non-UP Michigan. Its a truly unique region that is dissimilar to almost anywhere else I've visited; like mixing the cultures of the New England coast with rural farms.