No, we don't actually know anything about the structure of the game. Assumingly it will be somewhat similar to D:OS2 - Coop is still a thing, and devs want players to be able to split so there will be most likely fewer, bigger maps, rather then lots of smaller ones like in BG1&2. EA is supposed to come with a zone bigger then EA of D:OS2. But how the story will progress, and there will be any back&forth between locations is unknown. I can't really imagine they would d BG3 and not try to make a proper, central city, which you will visit, stay in and return to throughout the game. Comeon, your RPG is only as good as your city content.
They actually did come out and say it'll be similar to D:OS in that each act will be a zone, and you won't be backtracking. I assume this also means we won't be frequently entering and leaving the city of Baldurs Gate, but it'll be confined to a single act.
Now that would be an odd descision given its the namesake of the game. More likely Baldurs Gate will function as a hub of sorts where you can come and go all throughout the campaign.
Q: Like the original Baldur's Gate, will locations be broken down into sections or will it be like in DOS2, where you are in a huge terrain.
David: You're in a huge terrain, but between acts you will travel from one huge region to another.
Q: You have mentioned that the scope of Baldur's Gate 3 is huge, but we do not have much to go off of. How many places will we be able to visit and explore? Will it only be a small part of the Sword Coast or can/could we venture off to places like Neverwinter or to the South to see Amn? Is it closer to an open world or will it be closer to D:OS 1/2 in that it is a large map that is sectioned into smaller areas?
Swen: The small portion of the adventure we’ve shown takes place many miles East of Baldur’s Gate, and the initial journey will take players along the banks of the river Chionthar, and surrounding wilderness and settlements, toward BG and the coast. You won’t be walking the whole way to BG in real-time, so there will be several large, open regions. Later, you’ll visit the city of Baldur’s Gate itself, of course. Other places I’m not going to spoil for you because discovery and exploration are part of the joy.
This snippet of interview is interesting, but it’s not actually very clear how it’s going to work.
Both David and Swen use the word “Region”, but I’m not sure they are talking about the same thing.
David mentions traveling to different regions between acts, but Swen talks about there being several regions in the “initial journey” towards BG and the coast. It doesn’t seem to make much sense for that journey to take place over serval acts, so I think it’s more likely that Swen means that the journey is serval maps covering the river Chionthar, and surrounding wilderness and settlements, which is what David is calling a “huge region” (and therefore an act).
If so, I suspect that would be the same for subsequent acts. So maybe act 2 takes place in several maps covering Baldurs Gate and coast, which could well be the biggest part of the game. Perhaps then act 3 takes you further afield and act 4 brings you back to the city, or something?