Yes, agreed, 20,000 total land mapsquares. Minus Siberia. Minus the Rockies/Himilayas/etc. Minus the Sahara/Gobi/etc. Minus the Ozarks/Everglades/etc. And on, and on.
Ok every place you listed does have population and is capable of supporting it. Does that mean that there is much? No, but technology does change, even there. Siberia FE has, mainly because of Russia, better mining than it did before (course better is a relative term). The deserts have better technology for the people also. FE most defend themselves with rifles and pistols insterad of spears and swords. That's also not including stuff like oil, etc. The fact is you're assuming that since there are only a few people there and that they seem 'primitive' they can't change or adapt quickly and so you want to say they are unpopulated when they aren't. Like i said, there is a differance between unpopulated and minimally populated.
Someone needs to check some numbers. I can not believe Lordy's assertion that the Earths crust is near 100% populated (meaning, in this case, more than 1000 people in a 60m by 60m area).
There are differnt levels of density, but that is pretty much true, Most of those areas you mentioned above are nomadic areas (like deserts), sparesly populated houses like Alaska or small tribal areas (like Alaska and Jungles)
Even in modern times, with a 6 billion population, we have those massive mountain ranges, wide deserts, vast swamps, endless forests, etc that are not going to register pop in this game. I'd guess (based only on my own ignorance, but I'd like to see some actual data) that at worst we'd need to worry about 8,000 to 9,000 mapsquares, under the most amazing of conditions (unless, as I said, someone makes a 'Soylent Green' scenario).
Why? There are several reasons. First for political reasons. FE much of the SA jungle would be unpopulated as far as you're concerned, but they have enthic groups out there that are quite active now in politics to preserve the forest and their way of life. You can't do that if there is no population. Disease is also a factor as well as quelling local uprisings. Yes small numbers of people can do a lot. Use as slabve labor...most of those places you talk about have minorities in them. Most of what i said does haveto do with lower tech people, but they too can have influences even in modern times.
I guess you could have those squares designated as "minimal population" and not worry about the actual population number unless there seems to be a sprawl from an area that is calculated and then only change that to actual numbers when ness.