The world that seem most alik, geographically that is, are probably the nameless worlds of FFVII and FFVIII.

I can't help but notice that the desert in FFVII is roughly in the same location of the desert in FFVIII. Or the Great Salt Lake which is somewhere in the area of the Midgar Marshes.

Actually, they're just stupid observations. I don't really believe that the worlds are linked in any way shape or form.