[@Hexaflexagon] Oh gawd I hoped to avoid anything having to do with numbers. XD

I think of it as if one nomad tribe probably meets between one and three other tribes in a year -- possibly by design, in order to trade or fight over certain resources.

Essentially, miles and miles of empty space or wilderness, with probably mostly concentrated pockets of people in the areas least likely to kill them while they sleep, and even then they can walk for days without seeing another soul.

I'm not sure that's even an answer, but I'm sticking to it. :D