Metal Gear Solid 5's map has been compared to that of Grand Theft Auto 5's on Reddit.
The size of Grand Theft Auto 5's map is 6.63 miles multiplied by 4.73 miles which equals 31.39 miles squared. Of that, 350 map squares are water so once you remove that 12.55 square miles of ocean you end up with 18.84 square miles of land.
By comparison, The Phantom Pain's map is 2.48 miles multiplied by 2.48 miles for a total of 6.18 square miles. The game is set in Afghanistan which is a landlocked country so there's no deduction needed for sea areas.
This means that the total map size for The Phantom Pain is 32 per cent of Grand Theft Auto 5's map which is still significantly larger than what we've seen in past Metal Gear Solid games.
Metal Gear Solid 5: The Phantom Pain is set for release on PS3, PS4, Xbox 360, and Xbox One; you can check out our preview of the game here. After releasing on PS3 and Xbox 360 last year, Grand Theft Auto 5 is coming to PC, PS4, and Xbox One this autumn.