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.
