Arable land probably has to do more with carrying capacity in terms of agriculture and water resources. Yes, you could build a huge city on the Tibetan plateau

Arable land probably has to do more with carrying capacity in terms of agriculture and water resources. Yes, you could build a huge city on the Tibetan plateau but you would have to truck in a lot of stuff to keep people alive. Even the rural areas, you have to decide whether to keep them growing food (low density for China) or turn them into dense cites. Do too much of the latter and your cities starve. But you can’t really build cities on land unsuited for farming, since again you have to truck a lot of stuff in from far away.