If I'm world building and not just borrowing, then I go into decent detail. I have a set table of information I try to have fleshed out for every capital city and then another important city in whatever country. So in terms of that, it can get granular.
Cities usually go something like
- Brief history, population, population type
- Government type
- Law level (lax, moderate, authoritarian, etc), literacy level
- City culture
- Important places/holidays/NPCs
- Famous dish
- Intrigue
Some of these are left unanswered if they're too much, but I generally try to at least get a handle on how strict the law is, how smart the people are, and the culture and food. This helps me get a clear enough image to envelope my players in any one city. I personally also have a lot of fun trying to think of the dishes, ice flowers drizzled with fruit juices in this desert city, while an underground settlement has fried mushrooms and cow beetle steaks.
I also prefer to leave the imagery of a certain city up to an image as that can really inspire me to go from whatever I'm looking at.