Interesting. Speaking of that, I need to beat RCR, but the nes version. We all know the GBA version is scary.

The original "River City" was a translation quirk, the original Japanese had "Downtown" in that section of the title, instead (with the full Japanese title having a literal translation closer to something like "Hot-blooded Downtown Story").

As for the modern iteration, the canon explanation appears to be that River City is built primarily along islands within a river (with additional city on both of the banks of the river).

Related: https://en.wikipedia.org/wiki/River_island (though River City'd be more a collection of river islands, but there doesn't seem to be any real world example of that, with Venice being the closest real world example, with the key difference of in a lagoon rather than a river).

View attached image.