As you likely know, Super Mario Odyssey features a city based kingdom called the Metro Kingdom, with New Donk City being a major part of the region.
But while New Donk City is certainly important there, it's not all of it. Nope, the kingdom seems to stretch on for quite a distance outside of its boundaries, with the former being merely a small town on top of an even bigger skyscraper.
Which makes me wonder... could Diamond City also potentially be located in the area? How about other cities in the Mario series like the one from the Donkey Kong Game Boy game, or the Mario vs Donkey Kong titles? Or the one from Wario Land II?
Well there are cities in the Mushroom Kingdom. There's no reason why Diamond City can't be in any other kingdom. Who's to say there isn't cities in the Sand Kingdom somewhere?
There's just one problem. While you're flying to the Metro Kingdom, Cappy reads up on the place in his travel broshoures, and states: "the whole kingdom is one big city".
Well there are cities in the Mushroom Kingdom. There's no reason why Diamond City can't be in any other kingdom. Who's to say there isn't cities in the Sand Kingdom somewhere?
That may be true, but for some reason I think that Diamond City is located outside the Mushroom Kingdom proper. It looks nothing like anything in the Mushroom Kingdom with its much different inhabitants. And I don't think it is located in the Metro Kingdom either.
I can't see Diamond City being a part of the Metro Kingdom
After all, there's tons of cities in the Marioverse like Twilight City, Mushroom City,
Neo Bowser City, Neon Heights and various other cities, and they're most likely not a part of the Metro Kingdom either (Plus as WLGP said, The Metro Kingdom is basically implied to be New Donk City)
So unless they explicitly say or hint something regarding it, (Which is unlikely) I'll just say no
I imagine it's most likely it's own seperate island that's independent from the Mushroom Kingdom, Just like DK Island or Kitchen Island from the Wario Land games.
