I want regions based on something other than political boundaries. Even old ones.
SoHo and Tribeca?
Tribeca’s a fave because it’s a tortured acronym based on something that never existed.
There is the Mogollon Rim in Arizona.
And the Abert Rim in Oregon.
Rim is a not-often-used term to describe a geographical feature, and I dont think either of the above appear on most generally-used maps.
For that matter, does anybody talk about the Western Reserve, or even know what it means, any more? Except for people who work at or attend Case Western?
When I grew up in the Bay Area, The South Bay referred to the San Jose area, the South San Francisco Bay area. When I moved to Southern California, I was confused about what the people meant when they were talking about The South Bay. The South Santa Monica Bay area, El Segundo/Manhattan Beach/ Redondo Beach. Also, when people in the South Bay talk about The Hill, they’re talking about Palos Verdes.
My favorite is DUMBO, in Brooklyn: Down Under the Manhattan Bridge Overpass.
There’s also NoHo (North of Houston), Nolita (North of Little Italy), NoMad (North of Madison Square Park), and BoCoCa.
Yeah there’s a lot of stuff in northeast Ohio at least that is named “Western Reserve ____” other than CWRU. So it’s still in the region’s lexicon. And we do learn Ohio history in elementary and middle school where the origin of the phrase is briefly explained. But I don’t think the full meaning and ties to Connecticut are always stored firmly in our memories. But the phrase is there.
What do you mean? People who lived in a place needed a name, and constructed one by direct analogy to a nearby similar place.
I grew up in an area of the UK known as ‘The Black Country’. It’s not listed on any maps, and nobody can agree on the boundaries, or even the origin of the name. But it does have its own flag.
It is said to be the inspiration for Mordor, both in name and description owing to all of the smoke and fire from blast furnaces across the region.
Well… you could say that about every place name ever. 
SoHo seems to be the original of these place names, but Tribeca comes from “Triangle Below Canal”… which it is, sort of, as it is a triangular area topped by Canal Street.
Canal Street, however, was named for a freight canal into the center of Manhattan… that was never dug/built. The 1800’s version of Tunnel Three and the 2nd Avenue Line…
And it’s not even triangular
Well, it started that way, just as Nob Hill in San Francisco originally meant a house was, you know, ON Nob Hill. Trendy desire plus Realtors™, and you’ve got expansion.
Edit’s screwed up… consider that, technically, most of the US lives in SoHo. 
How about the Canadian Shield.
That article also leads to other geological region names like the Mackenzie dike swarm.
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There is the Northwest_Angle of Minnesota. Not accessible by land via the USA.
The Louisville, KY and Jeffersonville, IN area is referred to as Kentuckiana sometimes.
I believe Indyucky is a better, more mellifluous term.
While we’re in KY, how about the Pennyrile, covering chunks of the central part of the state, and the Jackson Purchase in the west?
Those administrative boundaries were themselves based on geography and language, and the second group of entities I mentioned (the comarcas) are sometimes administrative (and when they are, have well-defined limits) and sometimes not. There are places where asking people “where would you put the limits between X and Y comarcas” is considered a perfectly fine game for winter afternoons; rarely do you encounter two people who will place the boundary at the same spot.
Must confess that the possibility of Tolkien’s taking the “Black Country” of England’s West Midlands as a direct inspiration for Mordor, had never before occurred to me. I can hardly feel that the inhabitants would appreciate the implied likening of themselves, to Orcs…
I had, though, always been given a smile (without seeing the actual connection) by the passage in the closing chapters of LOTR, in which the hyper-gabby healer Ioreth, in the process of filling-in her cousin as regards what hobbits are all about, uses that exact form of words : “Why, one of them went with only his esquire into the Black Country and fought with the Dark Lord all by himself, and set fire to his Tower, if you can believe it. At least that is the tale in the City.”
Mayor Ben Bilboe of Bilston as an inspiration for Bilbo Baggins (as per link), though – while Bilbo is indeed highly eccentric by hobbit standards, it would seem to require a very great leap of the imagination to envisage him as a Communist and a Labour Party MP !
How about “Far North Queensland”? No-one can agree exactly where it begins, and depending who you talk to it could be said to start at Rockhampton, or maybe the Whitsunday region, or maybe Townsville. Everyone agrees Cairns is in FNQ, though.
Similarly, “The Outback” is another geographical descriptor that’s not all that well defined. Everyone knows if you head inland from any of the major cities you’ll end up there, but exactly where the border between “The Bush” and “The Outback” is subject to interpretation, in my experience.
Scablands of Washington State … always makes me laugh …