Okay, a few other people have posted, so time to give a small analysis of the region a try. Sorry for the blurry quality of the image, but it's the best Bulbapedia had. I touched it up with Paint to make it easier to comment on the specifics:
So: What we see is, I believe, the first area to be explored in the games. Allow me to walk you through it:
1) This is clearly the starting town. You see all the buildings from the trailer, as well as the little podium where you pick your starter.
2) Seems to be this game's equivalent of Route 1. It is fairly short, with no mandatory patches of grass. The trailer suggests there might be trainers there, or at least NPCs. I'm not sure if the player will start his/her journey in one of the houses in the starting town, or race up the hill to meet Professor Whatever and receive the starter Pokémon. The
first scene in the trailer suggests your bedroom has a bay window, which is not seen on any of the three houses
later on. It could possibly be found on the house underneath the 4) line, though.
3) The little waterfall here suggests there will be a small area here. I imagine something like the little pond at the start of ORAS, where you have a battle against your rival.
The trailer suggests there will be a path leading into the woods from the starting town, and I can't imagine
not ending up at the waterfall at some point.
4) This is probably a gate, and presumably the game's first roadblock. If I may hazard a guess: You can't pass until you've completed the segment with the little forest mentioned under 3). The building immediately after the gate may be the region's Trainer's School.
5) A little out of sequence, but that clearly is a cave opening. I'm not sure if the volcano will be the first cave you enter, or if it'll be a place you return to later in the game. They might pull a Sootopolis and have you Dive into it; the dark waters of the lagoon might suggest Dive spots. The fact that the lagoon has a closely defined border of rocks suggests we will be able to Surf there. A (presumed?) dormant volcano is also a good set piece for a climactic story scene.
6) The seaside town could be a location for the first Gym, or it could not. A little hard to tell, really. Presumably, there should be a Pokémon Center there, but I can't even make that out. So I'll skip the town for now. Let's instead focus on what is clearly a Route behind it. Note the quarry-like inlet in the cliffs, there might be something there. Maybe not something very interesting, since we're still in the early-game, but something nonetheless.
7) This appears to be another town on the far side of the island. If the first Gym isn't in the seaside town, it is probably here. The cliffs and caves beyond the town may take you full circle around the island, back to the starter town.
8) This is the main evidence for the existence of more islands: A ferry terminal, or at the very least a shipyard. I expect you to leave the island from here after
completing the tutorial beating the first Gym, or maybe the first two. It'll be a little like BW2, where you had your beginning area to complete before shipping off to the mainland. The terminal will be your Skyarrow Bridge, your Lumiose City or your Mount Moon; the game changes noticeably after you pass this point and take a step outside the calm beginning of the game. What we see in this picture is Beginner Island, we have only seen the first few steps of Alola so far. I can't wait to see more.
9) What is this thing? It's clearly outside the "surfing border", and it's a different colour from the stones in the bay. It appears to be
something, but it seems inaccessible. Anybody have any ideas?
