wildland. A Sub-city may be built on it. However, unlike other wildlands, flatground contains no resources. Exploring flat grounds will yield an amount of gold, depending on how long it is explored for, and possibly items. To build a Sub-city on a flat ground, you must occupy it, have 100,000 of each resource (food, wood, stone, copper and gold) and be at least a Senior Prefect. Additional sub-cities may be built at higher positions. Also, it is possible to use divine wind to move one of your cities to an unoccupied flatlands or fated wind to move one of your cities onto a random flatland in a selected region.
A famous city cannot be built on a flat ground. It is different from a normal sub-city as it has to be captured and has skilled, expert or master troops defending it.