South Australia has a population density of 1.7 persons per square kilometer...approximately 1.7 million people spread over a million square kilometers. The surface area of the earth is 510 million square kilometers and the equivalent population at that density would be less than one billion if people could inhabit the ocean surface. However the land surface is only about 150 million square kilometers including Antarctica. The Earth's land surface population density is 52 times that of South Austriala. Even the absolute population density is 15 times that of South Australia.
A lot of people would need to never be born to create an environment with similar conditions to the model.