My fear in Civ6 is that with the new districs system cities will occupy a lot more ground than in previous games. You will also still need the farms/quarrys/mines/oil/etc tiles besides the distric tiles.
If maps are not big enough to acomodate that, specially Earth maps for TSL games you could find yourself i.e: only being able to place 6 cities max in western Europe landmass because you need the tiles.
You may need more cities to build different districts and wonders, but cities occupy the same amount of ground, which is a 3 tiles radius.