A moratorium is in effect on adding information from Fire and Blood until December 20th.
The Flatlands are bordered by the upper reaches of the Rhoyne to the east, the Velvet Hills to the north, and the Golden Fields to the southeast. A Valyrian road runs through the Flatlands from the Free City of Pentos to Ghoyan Drohe.
The Flatlands is a fertile area of open fields and plains, located around Pentos and responsible for feeding it. Tillers and toilers who are bound to the land dwell in the Flatlands, while many magisters and nobles of the cities have estates on the Flatlands. Illyrio Mopatis owns some orchards, farms and mines in the Flatlands, though he seldom visits them.
The Dothraki can easily access and ride through the Flatlands, so Pentoshi magisters, like nobles of the other Free Cities, pay them heavy tribute so as to ensure they do not loot or sack any of the estates or villages in the area.
A Game of Thrones
A Dance with Dragons