I was always under the impression that Sinnoh was what happens when you do have a large combination of different ecosystems and stuff.
Sort of. Except, well, it's actually possible to do that without having to leave a real-world location. (For reference, Sinnoh is
based on Hokkaido. Check that link to see what each city is actually based on.) It's possible to have drastic temperature (and therefore ecosystem) differences between two neighboring real-world regions or even two different areas within the same region. For example, Boston tends to be warmer than western Massachusetts, but that's because of the benefits it gets from being right up against the ocean, rather than further up in the mountains. Then you have a place like Pennsylvania. The western half tends to get a crapload of snow and bitter-cold weather (thanks to both the Appalachian Mountains and the lake effect coming from Lake Erie), but Philadelphia and eastern Pennsylvania tends to be flatter and warmer. Heck, you could even say the same about California and how different Los Angeles is from San Francisco in terms of climate, geography, demographics, and... actually, yeah, pretty much the entire list. So, yes, you can think small and still get the same geographic variations, so long as you do your research.
That and there is, of course, room for artistic license, but deciding it always snows in a city based on a real town in northern Hokkaido isn't the same as basing a city on Las Vegas to get a desert area and another city on St. Paul to get one that's always cold.
I always imagined that region to be the largest just because at the very least when I played through it, it had a large value of ecosystems (a temperate area, a cold area, a mountainous area, a desert area in the upper right island, a volcanic area, a marshy area).
That would be because real-world Hokkaido
does have all of those geographical features.
(Well, that and you're correct. Comparing each of the first four regions to a map of Japan, Hokkaido
is larger in area than Kanto, Kansai, and Kyushu/Okinawa. But it's not as large as an entire country.)
A lot of the cities I named are all in a temperate areas.
That would be because most of the United States is in a temperate zone. So is most of Canada and half of Mexico. (If we want to get particular about details, then you start dividing up the continent into tons of different regions, but we'll get to that in a second. Including how Chicago and Indianapolis are not even in the same climate regions as Philadelphia and New York.) That still doesn't mean you should squash everything because what defines a region isn't
only its climate.
Actually, yeah, that's a point I'm a bit confused by. Genuinely, too, so I don't mean to come off as too harsh here. It's just that my point was "don't smash a massive country into one tiny region because there's extreme differences in
culture between each actual region and state." So how did this turn into "you should because all of the cities have the same climate"? That and I'd like to know how climate is actually relevant to whether or not a bunch of places should be condensed into a region, particularly given the point that you've said in your first paragraph that Sinnoh is an example of where cities
aren't similar to each other in that regard.
So, it would make sense to squash the area because the areas are actually similar enough (I mean is New York, Chicago, Philadelphia, and Indianopolis too much different in climate?).
Actually... they are. Chicago isn't called the Windy City for no reason (and it actually has more extreme weather patterns thanks to being right up against Lake Michigan). Indianapolis gets extremely hot thanks to being smack in the middle of flatlands. New York's temperature and weather patterns are regulated by the ocean. Philadelphia is... probably actually closely linked to New York. Even then, if we want to start being really particular, while Chicago and Indianapolis share a climate category (i.e., they both experience humid continental climate), New York and Philadelphia are part of a band known as humid subtropical (yes, which it shares with the Southeast) and therefore are literally on a different wavelength than the inland regions of the continent.
I know they have different characteristics that are there because of their locations but you can make it work somehow.
Not really. That's a lot like saying a New Yorker is, at their heart, the same thing as a Bostonian. (Tip: Don't try implying this to strangers in either city. This is a good way to start a fight.) The reason why I make this comparison is because canon's already made it. An Osakan (or someone from Goldenrod City) is not the same thing as someone from Tokyo (Celadon or Saffron). There's a lot of history and a lot of rivalry between both regions, and both cities are particularly proud of their unique cultures. That extends to the rest of Kansai and the rest of Kanto, which is why, instead of creating a map based on the entirety of Japan, the development team separated Johto from Kanto. The same could be said for the United States -- which they've already started in on with Unova (New York City) and Orre (Arizona). Simply put, the United States is just too big with too many cultures and regional variations all at once to cover in just one map, and the game developers have already realized that.
Granted, there are lesser-known fics that have
tried to do things like condense the entirety of the United States or Canada into one region, but think of it like this also: your character will have to travel extreme distances to get from gym to gym. If you want to base an entire region off the United States, you might as well do it right by bringing up the fact that your characters will have to get through Kansas to get from Chicago to Houston, Utah to get from Houston to California, and so forth. If you don't want to bring up that much territory, then chances are, you'll want to think small.
The point I wanted to make was not "Use these cities" but "Look at what these cities have, you can make new cities if you stereotype the cities and put it together in a new city"
Every region is based on a real-world location, and even then, given the fact that the OP wants to use an existing city in Ohio as his starting point, it looks like he
is going on some level for accuracy.
There is one question I have... Castellia does not at all look like a city that is situated right next to the desert. It seems kind of dissonant to have a bustling temperate zone seaport right next to a desert... And right across the water from the city is a forest. That are just doesn't make sense to me: the whole closeness of the desert to a major city. So, I don't doubt that the designers might have done the same thing: compress a country into a region sized area... ... ...
Again,
Unova is based on New York. Pinwheel Forest is based on the forests and parks that are actually scattered around the area. (You can check out a decent comparison
in this video. There's another one that
shows you just how varied New York City is in terms of landscape.)
Point is, you
can base a region off a real-world location, but as you've said, you've got to do a ton of research into it. And if you do a ton of research into it, you'll probably find that sometimes, cities and locations shouldn't be lumped into the same pot. That's why Unova is basically
only the New York metropolitan area, not the entire state of New York or even the entire (real-world) region of the Mid-Atlantic. There's just too much to it to allow it to be condensed down into a single point of a larger region. Someone from Brooklyn isn't going to be the same kind of person as someone from Midtown. You could go with a general stereotype of the entire city, but then that would seem like you're glossing over large swaths of detail. There's a reason why the in-game regions and locations themselves are so interesting: because the programmers always pay attention to detail. So by zooming out and saying that everyone from Boston (Southies, the people from the North End, folks in Cambridge, other folks in Roxbury, and so forth) are all the same just so you can stick Boston on the same tiny map as Los Angeles, you end up missing a lot of what makes a region a
region, if that makes sense.
Edit: I guess a good way of putting it is that basically, while everyone has an allegiance to a country and while everyone has basic similarities that way, region tends to be more specific and hones in on a place where people's attitudes tend to be similar. Think of it like this: a country is you and all your neighbors, whereas a region is your family. You may be friendly with your neighbors because you all live in the same place, but you're closer to your family members.