Most likely it will be the final map of the game. Same way Arx was in DOS2.
Going with hints Larian people gave in the past, it's supposed to be the focus of "Act 2", which in itself is supposed to be "the biggest Act by far" out of the three that are going to structure the entire game.
One thing I can already tell I won't be trilled about is having the city frozen in a single moment in time (like the rest of the game) and without a single hint of a day/night cycle.
You'd imagine exploring the streets of the city in daylight and when the night falls, looking at street lamps turning on, being careful of not being ambushed by thugs in dark alleys, etc, etc...
Instead Larian decided that the whole day/night thing, that has been a standard feature in the genre since the days of the Ultima series, was some fanciful waste of resources compared to CORE features like "I can replay the game as one of my companions".
So no Baldur's Gate at night for us.
What a bummer.
what was novigrad like? i quit witcher 3 before i reached it?
In terms of 3D modeling/assets/details? The golden standard for a medieval big city in a RPG any title in the genre should aspire to.
Not exceedingly interactive, on the other hand.
Stuff like Gothic 2 and Ultima VII did more for immersion, if on a smaller scale.