If you look at what I've been doing, I'm the only player in my city and the only details I was given from the GM were "artistic" and "tropical", so I took what those words evoked in my head (based on the current time period / world setting) and mixed them together with how I wanted my character to grow as a person and with her career, and created the City of Kruvaria for Ermeline and future roleplayers to explore! Now, if someone else had already been in the city, I'd be more careful about describing the entire place like that - I'd have read what the others had said and added my own impressions and little details to what's already there - like that the alley next to the (already-established) blacksmith houses stray cats, or that my character loved the apples from a particular vendor in the marketplace. If your character wants a honey bun, and a pastry shop has already been mentioned, it'd be cool to go visit that store - but if a pastry shop hasn't been mentioned yet (and it makes sense where you are) then write one into the world! It can be a bit tricky to not overstep your boundaries, but really, I'd say go for it and get reprimanded later :P
Also, if you're confused where everyone is, try going back a few pages (doesn't have to be the whole thread) and see where people say they are. Might have to cross-reference with character sheets to know which city, since not everyone is starting their posts with that information, but it's usually pretty straight forward (unless people start getting confused and teleport around. Can't help you with that!). I think I'll start adding a little location blurb to the start of my posts to help with that :) Especially once we start having multiple characters per person.