It might be tempting to write off Koriko as a one-time thing, intricately realized because the story demanded it. But this underestimates Miyazaki’s commitment to world-building. In another early film, Castle in the Sky (1986), a good portion of the movie is set in an unnamed mining village with terraced houses overlooking cliffs. Not only is it beautiful, but when the character Pazzu is attacked, the whole village comes to his aid; lights fill every window and miners fill the street.
Then in Porco Rosso (1992), Porco takes his damaged biplane to Milan to have it repaired. He doesn’t go to the touristy part of Milan. There’s a canal, a bunch of warehouses, and other mundane infrastructure and uses. It’s the polar opposite of Koriko. But what ends up being important is the community Milan supports. Porco’s mechanic, Piccolo, is able to draw upon his relatives in the area to work on the plane and feed everybody.
It is Miyazaki’s emphasis on the human inhabitants of his cities, and the communities they form, that sets him apart from too many real urban planners. He creates cities that are wonderous to behold and to be in, places where people can form strong bonds with one another. His cities are designed to accommodate characters behaving like humans, not maximize vehicle throughput or home values.