Some of you people sure do get upset when someone suggests Los Santos is small. I figure if I bothered you so much, you'd want to shut me up or make me look like a fool and the best way to do that would be to show that my estimates are baseless and inaccurate. No one has because they can't. Every argument against me is based on unlikely assumptions. The person who made some claims was unable to back them up and has shown that he's probably a liar.
All of my estimates are objective. I'm not skewing anything to make the map look small. Some more stuff...
Back to this pic - http://i.imgur.com/wfb8w.jpg
The ship picture is in first person. The Statue of Happiness is in third person camera mode. Even taking into account the size differences of background objects in different perspectives, the size differences increase/decrease at a greater rate than distance traveled. For instance, a short distance on the map has a large effect on the sizes of objects. If two similarly sized objects appear to be the same size in different pictures, then they're probably about the same distance away. Perspective can alter that and we'll get to that later.
In the above image, the distance from the ship to the Empire State Building appears to be about the same as the distance from the oil well to the Bank Tower. It's unknown if the oil well picture is in first or third person mode. It's probably in first person since that would make the city appear larger.
Anyway, here's a large size of the ship picture from the trailer - http://i.imgur.com/sRDSl.jpg
Here are a couple of pictures I took from the same spot. One is in first person like the trailer and the other is in third person...
Assuming the oil well picture is in third person, you'd have to add that extra distance above to the known distance from the ship to the Empire State Building to get a decent estimate of the distance in the oil well pic.
Applying that to TreeFitty's map, you get the maximum estimated size here:
If the oil well picture is in first person, TreeFitty's map would be significantly smaller.