So to get a feel for population density, a rough eyeball for Sartar (including the Dragonewt Wilds and the Far Place) is about 7200 square miles or 18,900 square kilometres. If we ignore the dwarves and any purely temporary groups, there are about 194,000 sentients living in Sartar, which gets about 27 people per square mile or about 10 people per square kilometre. That’s about basically the norm for a low density agrarian society and about half the density of Classical Greece (see Zimmermann, Andreas; Hilpert, Johanna; and Wendt, Karl Peter (2009) “Estimations of Population Density for Selected Periods Between the Neolithic and AD 1800,” Human Biology: Vol. 81: Iss. 2-3, Article 13. Available at: http://digitalcommons.wayne.edu/humbiol/vol81/iss2/13). Which seems about right given how urbanised Sartar is (Boldhome, Alda-Chur, Wilmskirk, Jonstown, Swenstown, and Alone, plus numerous smaller towns).
Lunar Tarsh, which covers a roughly comparable area, has a population of roughly 18 people per square kilometre, or 50 per square mile. That’s roughly high medieval France or actually about the same as Classical Greece.
Also the Oslir river valley from Dunstop to Talfort is quite densely populated. The rest is more like Sartar.
So basically, what you can get from this is that Sartar has a bunch of agrarian valleys that might have a population density of 18 per square kilometre or almost 50 per square mile. Or more. But then you also get a lot of empty – the Quivin Mountains, the Thunder Hills, the Forloss Hills, the Yellow Hills, and other woodlands.
Remember, there are roughly two or three hides per square kilometre. So an average clan occupies one WBRM hex, that means there are about 130 hides of cultivated land, and another 70 hides in herds and livestock, per cultivated hex.
Given that it takes about 1 hectare of cultivated land to support 1 person (as the Sartarites are not intense agriculturalists), we can crudely estimate that about 10% of Sartar is under cultivation. Which just happens to be about the same percentage that Matt Ryan’s master map shows!