This reminds me, I think the normal measures of population density aren't very helpful, but I'm not sure what to replace it with.

If Alaska seceded, almost nobody in the other states would feel the difference, but the population density would jump 15%: https://www.wolframalpha.com/input?i=%28%28population+USA+-+...

(Or in reverse if Trump acquires Greenland — with no real change to people's experiences, the population density would go down 23%: https://www.wolframalpha.com/input?i=%28%28population+USA+%2...)

Likewise Australia, the outback is about 70%-85%-ish of the country depending who I ask, with about 607k people in it, so if the Aboriginal Australians were to secede with it, the rest suddenly gets x3-x6 the population density with no actual change to their experiences.