If you could do population management at a worldwide level, you would look at the current density and available resources, yes? That would be the most viable and survivable solution. Perhaps tweaked a little towards actual habitable land, because steep rocky mountains can be pretty hard to try and survive on. But that’s besides the point;
We’re already at 508(!) humans per km2 in The Netherlands, in Canada by comparison that’s 4 per km2, in the US it’s 33 per km2, in France 106/km2, on Ibiza 227/km2 and in Denmark there are around 132 humans/km2. Just some examples. I find it absurd that not one world leader with half of a brain comes up with decent dividing of habitable land by now. Not even a proposition to that end. Hell no; All they’re doing is pulling up walls, protecting resources for their own, keeping it for themselves (and preferably with underpaid slaves working and producing for them at the other side of the wall).

Nobody inherited land on earth, they’re all just pretending to have ownership of it. This (strictly human) game of pretend ownership will all come tumbling down when shit hits fans in densely populated areas, when mass migrations will be the unavoidable norm. And the masses will know exactly where the least densely populated areas are, because food options are better there!
The Netherlands *should* therefore be a totally uninteresting area to want to move to. There’s no food (options) here, there are huge waste storage, recycling, sewage and pollution issues, because the land is too densely occupied by humans already. The NL relies on 17 times its own land area to feed its population. At some point in time we’ll have to divide habitable land over the remaining humans equally, not like it is divided now. Our population density would be enough ground for a radical stop to immigration, yet all they do is make it a right-wing xenophobic issue, which will make it impossible to even discuss this issue in Dutch/global politics properly.
The end-result of our current non-strategy regarding population management will be that the crowded areas will be forced to arm and protect themselves to the extreme, where each rich family will build a castle with enormous security shields around it, so they can keep growing food on their ‘property’ and survive. Is that what we want?

The great golden new-lib way that supposedly works miracles for any economy seems to have made mush and mulch of many “rock star economies” to the extent that the filthy rich land owning nations can’t afford basic social welfare improvements or even local refugees. Which is all utter nonsense: We know it’s just that the neo-libs currently in power and paid for by the Big Corp money boys (fossil fuels and big agri livestock industries) want to avoid setting a precedent ’cause they know what’s coming down the road, and it’ll soon enough turn into an endless flood of humanity once they open the doors. Which should be done anyway, especially since it was us first-worlders who turned the thermostat up and broke the machine to begin with.