There is the measure of "arable land" which isn't too close, but explains a lot. https://en.wikipedia.org/wiki/Land_use_statistics_by_country https://en.wikipe

There is the measure of "arable land" which isn't too close, but explains a lot. https://en.wikipedia.org/wiki/Land_use_statistics_by_country https://en.wikipedia.org/wiki/Land_use_statistics_by_country Land in permafrost, desert, mountain or swamp isn't arable and can support by itself a lot less population. This doesn't matter as much at a today when food can be shipped anywhere.