Greater Hexi is a small nation/kingdom located in the south-central part of Roshar during the Era of Solitude, between the Tarat Sea and the mountains where Urithiru is located. It is bordered by Tu Fallia to the northeast, Marat to the south, Emul to the northwest, and mountains to the north ... though there are no apparent geographical features that dictate these borders. The island on the Tarat Sea that lies just off the coast can be assumed to also belong to Greater Hexi.
The windswept flatlands of Hexi are not unlike those of Dalinar's homeland, but strangely, there isn't a rockbud in his sight. The ground is covered in wrinkles, like frozen ripples in a pond, perhaps two or three inches deep. They are crusty on the stormward side, covered with lichen. On the leeward side, grass spreads on the ground, flattened. The sparse trees there are scrawny, hunched-over things with thistle leaves. Their branches bend so far leeward, they almost touch the ground. It's like one of the Heralds had strolled through the place and bent everything sideways. The nearby mountainsides are bare, blasted and scoured raw.