Do people even look at the fucking map? By Odin's beard. The map is clearly populated with points of interest.
I love the scale comparisons and perspectives that have been posted, it's just amplified the excitement ten-fold. I absolutely could not agree less with people's comments regarding a necessity for a good fast-travel system, personally, because I very rarely found traveling around any of the GTA maps unenjoyable. Can we get some positivity for Rockstars masterful map crafting in here? I imagine taxis will make a reappearance as the main mode of fast travel, like in IV. Maybe buses too, that could be quite funny.
Oh and GTA maps are islands, that's just how it's always been. I think they'll probably explain the disappearance of San Fierro and Las Venturas with an earthquake that separated Los Santos from San Fierro at "Flint" area (Flint Water, Flint Intersection: http://images4.wikia.nocookie.net/__cb20130504154239/gtawiki/images/d/d2/Gtasa_areas.jpg). You have to use your imagination a fair amount, and rescale the San Andreas map in your mind, but it could happen... in video games.
I'm genuinely really enthusiastic about GTAV, hopefully this optimism isn't misplaced.