You know what was cool about Left 4 Dead 2? You could play Left 4 Dead maps with it (you could also play it while still boycotting it , which was convenient). Turns out, that's also what's cool about Civilization 5 - all those maps of Faerun you were working on will import right into Firaxis' upcoming turn based megalomania sim.
Here's a diagram:
On the left, a square. On the right, the almighty hex (which is short for hexagrammathon). They are different shapes. I'm not sure how I'd even begin to turn one into the other, but then again, I'm not Jon Shafer. Jon Shafer is, though, and he's just told Bitmob that you can "import Civ 4 maps into the world builder and convert them into Civ 5 maps, including all the units and cities and stuff on it - the conversion process will just do that for you automatically. We're hoping that the first week Civ 5 is out, people will use that function and port all of the Civ 4 stuff over to Civ 5, so everything will be out there already."