sort of real subcontinent inside of pavala, north of tebua, west of Ganuo, east and south of the rift zone. it is geographically a very large endorheic basin with all water falling inside of it flowing to the Hac Sea. the seas and areas around have very small river valleys in comparison.
it had one of the world's first civilizations forming <<on the river/on the coastline of the hac sea, climate>>. since then the tendency in hac has been for states to expand inland along hac's largest river and around the sea and have tributaries further afield. there are often smaller more shattered states further from its largest rivers, and frequently multiple states control the coastline of the hac sea (maybe 50-90% of the time). the current world-historical situation of hac is quite a shattered one other than Atra.
the area in the west near the rifts has been the escape hatch for many a people in decline, and so that is where the greatest cultural and linguistic diversity lies. hac tibet has been more like the hac region for most of world history, but in more recent times ganuo has sometimes controlled it, including at the present. it is less diverse than the rifts and has one main river valley that the plateau's culture and history revolve around. the higher you go in elevation on hac tibet, the sparser the people and history, and large portions of it are populated solely by nomads.
there are at least three language families in hac, the largest is simply named Hac, it should be spoken by 80-90% of hac residents. there is a second smaller language family spoken by most of the rest, then a third even smaller one scattered in three to six languages in the rifts. the nomads of hac tibet should speak an isolate, that is actually descended from proto-hac 3, but the evidence for this in-world should be unrecoverable. additionally a few Rifts-Ganuo languages are spoken in the northwest area in the hills and mountains.
technologically, hac was in relative decline to the rest of the world until recently when haki exploration became serious, and now the trend has only been reversed near the sub-Haki point. it started out way ahead of most of the world with its initial civilization which came before Ganuo had organized at all. they pioneered the beginnings of mathematics, astronomy, and so on. there are some fascinating artifacts that have been discovered from the early hac civilization that imply some knowledge of chemistry too, however, most of this knowledge was lost during the hac dark ages, reverting to more aimless alchemy.