The City will be a large level, currently, one area is built based on the Rooftops level. Others areas will be added over time.
The concept is that other mods/packages can use this level.
Note that this on its own doesn't have any objective, this is basis for other mods, you need to install other city level based mods to actually play.
TCTF HQ building is added to the level. You use the BINACJBO files from level 8 to add furnitures, doors, consoles, patrol paths and so on, without modification to their positions.