1000 square feet per person, for an apartment with a large balcony, is very comfortable.
For 10 billion people to have 1000 square feet is 10 trillion square feet.
With 10-story buildings, 10 trillion square feet would require 1 trillion square feet of land.
1 trillion square feet is 92,900 square km…let’s round that up and say 100,000 square km.
Throw in another 60% more land for roads, parks, etc. – also a very comfortable amount, especially if you don’t waste most of it on cars – and you get 160,000 sq. km.
160,000 square km is a square with sides of 400 km. It is about the size of Wisconsin, or Tunisia.
In Canada alone, there is already an estimated 126,000 square km of urban land.
If you don’t like living in a spacious apartment 10 stories high, but prefer instead that your city have 5-story buildings, you would need 2 trillion square feet of land for apartments. That’s 186,000 square km of land. Add another 60 percent for public space and you get a bit under 300,000 square km. That’s a square with sides of about 550 km. That’s the size of Arizona, or Italy.
Whatever else we may lack, space is not it.