I'd say we think of the "Midwest" because it's flat and the "South West" because it's sandy and hot. These clearly are geographic regions, like Pacific Northwe

I'd say we think of the "Midwest" because it's flat and the "South West" because it's sandy and hot. These clearly are geographic regions, like Pacific Northwest, (which has evergreen forests and mountains). If your point is these regions would have different cardinal names if borders looked different, that might be true, but that's not exactly profound and it's certainly not a matter of a "politico-cultural fascination with that border in particular."