Once upon a time, my gaming group and I had a massive, mega-combined world that at least three of the primary GMs used for our setting that we called Chornalth. (See below). Originally, it contained adaptations of the maps from the three primary D&D worlds, Oerth (Greyhawk), Toril (Foregotten Realms - though beaten and skewed), and Krynn (again, beaten and skewed). Our original map looked something like this....
CHORNALTH WORLD MAP
However, the current campaign has already
determined that the gods, in their infinite incompetence and general
inability to get along without mortal heroes, will be splitting the
world into three, equidistant worlds, orbiting the star known as
Chornalth. The three worlds in question are going to be known as Liga
(Oerth), and the other two GMs have yet to figure out what they're
going to call their worlds. I'm in charge of Liga...