The way it works at present is that both the strait and the isthmus exist - that is, land units can cross, as can sea units.
Cheers
Cheers

I also really like the hills, and the mountains seem to work fairly well. I can't say I like the plains or forests that much compared to the other ones. But your forest should work better with roads and such. IMO the new sea is a bit too subdued.
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