i think that if you mash Liberty city together, and get rid of the water inbewteen the islands, I think thats the basic size of Los santos. i know the forest wll be pretty big, but around LA there is more of a presence of desert. so i think the desert region will be the largest. The prison will be pretty large also, but i dont expect it to be a major part of the map. I do expect for a desert airstrip, like GTA SA, and i think that grapeseed will be up in the foothils of the moutains and the forest, possibly in a U shaped valley with the mountains surrounding it.
the maps ive seen are also very linear.IMO the map will be spread out up and down, but also to the east of the city. The desert ( like ive stated above) is a major part of So-cal's geography, not as much as the mountains above.
Some large Salt Flats would be good as well. Since the real L.A. has something like that nearby, and because I would like a large, flat and open space to test out the performance and top speeds of some of the better cars.