Okay I now possess BG: DiA and it has a fair sized Gazetteer on Baldur's Gate and it explores other areas and possible events and machanics that will likely impact BG3.
The Gazetteer was honestly better then I expected, soooo many interesting plothooks and 5e made Baldur's Gate way more interesting then it used to be thanks to the cool outer city (which honestly should have gotten more space).
Spoilers Alert Below:
Baldur's Gate feels less like a unified City like Waterdeep and more like a metropolian area of 4 linked cities, with upper, lower, Little Calimshan, and the rest of outer districts.
My favourite districts are Bloomridge, Temple, Little Calimshan (part of the Outer District, walled off, very Calimshan flavoured), Twin Songs (Religious District, with mental health retreat), super inhuman Sow's Foot (those worried about how more monsterous humaniods would not be killed on sight by BG, Sow's Foot is mostly very exotic, with like Lizardfolk and the like in it).
There is also a Hospital in Baldur's Gate staffed with Clerics from all sorts of Religions, even evil ones, so that is very interesting in a lot of ways.
Also possibly the funneist place in BG, Undercellar is like a Cross between a giant brothel, illegal market place, tavern, ect..., it has it's own police force if sorts (so does little Calimshan). There is a huge Chessenta style Bathhouse that is also basically a brothel as well, although it does have other uses.
So many different groups function in the city.
A lot if really cool BG backgrounds.
Twin Songs allows shrines of any religion, even evil Gods and Fiends as long as no violence is committed. Most religiously diverse district of BG, the way Sow's Foot is the most species diverse region.
I'm just scratching the surface so far. Like there are stables with exotic animals like Owlbears.
