Alright, so let's guess the map size of GTA V. To do so, keep those facts in mind:
1.- Map sizes of previous GTAs
GTA III: 3 square miles
GTA VC: 3.5 square miles
GTA SA: 13.6 square miles
GTA IV: 6.8 square miles
2.- Rockstar statement: "largest and most ambitious game we've ever created", meaning that it's larger than San Andreas.
3.- Planes are shown in the trailer several times, and planes require a large map. Significantly more than IV and at least as much as San Andreas.
4.- If we assume that GTA III compared to San Andreas is the same than GTA IV compared to V, by rule of three it results 30.8 sq mi. This has no reason to be true, but is an intresting way of seeing it.
5.- The size of some of the biggest games:
Farcry 2: 31 sq mi
Just Cause 2: 400 sq mi
Test Drive Unlimited: 618 sq mi
Test Drive Unlimited 2: 839 sq mi
Fuel: 5560 sq mi
6.- Map size is not the only thing that makes a videogame good!
SO, LET'S VOTE!!! =D