As someone of the earth sciences it is my opinion that whoever drew this has exactly zero understanding of “natural geographic borders”.
I still like this version of a natural American borders:
Eh!!??!! Stay on your side of the 49th parallel!!
My heart wants to like this on principle because that’s how geography should be divided, but it looks like garbage. I never really stopped before to appreciate how tidy and professional those arbitrary perpendicular lines look.
What specific geographic borders were used? Or is it just sort of random to look organic?
I can definitely see the Mississippi River still, so I don’t think it’s watersheds. Unless they’re using peaks and troughs both. I’m sure there’s a term for it. My understanding of water shed is that it means everything that flows into a river so a river would be in the middle. So the borders of watersheds are more like mountains than rivers.