About 9 out of 10 Americans live in cities (incl burbs) and the same holds for Australians. Sure, there's fewer notable population centers in Australia (Sydney, Melbourne, Perth, Adelaide, Brisbane and you got nearly everyone), but there's also just 10x fewer people than in the US so that kind of matches too. I think the picture you link to distorts this, it does not account for the fact that there's simply way fewer Australians.

I'm not convinced that if there were 300m Australians, that they'd still all live in those 5 cities (with every city being 10x bigger). I think there'd be more of them.

That's a rather expansive view of cities based on what the US Census categorizes as urban vs. rural. Between myself and a couple neighbors, we're on close to 100 acres, but that's urban according to the census because we're not that far from a major city and fairly close to some smaller ones.

> I'm not convinced that if there were 300m Australians, that they'd still all live in those 5 cities (with every city being 10x bigger). I think there'd be more of them.

I don't think so either, but because of the climate and geography, I also don't think there'd be 10x more cities, similar populations, I think you might end up with 2-3x more, really, at most.