The out-of-universe reasons Star Trek is not as diverse as Earth overall are obvious.
But it has always striven to be.
Yet if I think about all the places portrayed on Earth, they are overwhelmingly in North America (and Europe).
Are there any counterexamples?
Some locations on Earth which come to mind off the top of my head:
- San Francisco (Starfleet Academy, 19th century Guinan, Star Trek IV)
- New York (TOS: "The City on the Edge of Forever")
- New Orleans (various episodes related to Sisko men)
- Iowa (young Kirk)
- London (Star Trek Into Darkness)
- France (Picard's vineyard, Federation President's Office)
- Los Angeles (Voyager "Future's End")
- Nevada (DS9 "Little Green Men")
- Pennsylvania (ENT "Carbon Creek")
- Montana (Star Trek: First Contact)
- "The Arctic" (ENT: Regeneration) -- based on the names of the researchers, I'm going to assume this is Alaska or Canada, but at any rate, there is no other Earth culture here
- Florida (ENT Xindi incident)
Clarification: Portrayal means an actual on-Earth scene occurs in a location.