For my calculations I used the map from here:
http://gtaforums.com/topic/531982-very- ... map-sizes/He made very precise calculation that prove that GTA SA is the biggest GTA map pre-GTA V and detail the scale of the map
Instead of putting a rescaled map of RDR/IV/SA on a 1982x2644 map I decided to compare them with exact size according to their scales.
And the leaked map from here:
http://i.imgur.com/7BgHpKO.jpgI used the Photoshop ruler tool to find the following:
From his calculation in the picture, using the golden line scale: 273 pixels = 1 mile = 1.60934km
In GTA V's leaked map scale on the right size(5000ft - The part you can see in the middle): 76 pixels = 2250ft = 685.8m = 0.6858km
So I needed to find out how much is 1km by using percentage calculations:
GTA V: (76x100)/68.58 = 110.8194808982211 (Pixels per km)
GTA SA: (273x100)/160.934 = 147.2653386 (Pixels per km)
I then made the GTA SA map from his thread 110.8194808982211/147.2653386 = 0.752515467 = 75.2515467% times smaller(Using photoshop resize percents when you CNTRL+T) to match the size of 1k in GTA V's map to see the size comparison
This is the result:
http://i.imgur.com/0q6hht6.jpgIf Rockstar used an exact scale when printing out the manual this is pretty insane.
As the guy in the thread I linked to said, ""GTA V is larger than San Andreas, GTA IV and Red Dead Redemption combined" statement means that it could take over HALF AN HOUR to jog from one side of the map to the other" but he used the number Rockstar gave of square km that might include water.
Anyways, it's pretty big and if you didn't believe the pasted maps one upon the other like I did, you have proof now.
It looks even bigger now seeing as the GTA IV map someone posted here covered half of the map while after doing some math, the GTA SA map that is bigger than GTA IV covered barely Los Santos.\
Edit: A good point Jennica pointed out: There's underwater distance to factor in and if most buildings in LS that has the same size as the whole San Andreas map have interiors, some with even with second, third etc. floors, this is insanely huge. That's too much to calculate without more information from R*.