[NorthernSanctuary]

The numbers are a little bit off:

total area require = Area/person X 6.4 billion.

If you use 10 yard2/person= 90 sq. ft/person (1 yard =3 ft, 1yd2=1 yd x1 yd=3ft X 3 ft=9 sq. ft)

total area = 9X6.4 billion sq. ft.=57.6 billion sq ft= 57.6 x10 9 (power of 9)

1 sq mile=3,097,000 sq. yard=27,878,400 sq. ft

total area= 57.6 billion sq. ft X 1sq mi/27,878,400 sq. ft=2,045 sq mile. or within a city that is 25 mile wide by 25 mile deep.

The assumptions are wrong and not realistic in the required area per person. People need food, so you need room to grow that; the meat that people eat need more space also. Also a building takes more space than the living space. also energy production, transportation room etc. You have to look at the eco-system that is required to support the people, not just the people living space. Having said that, it may be possible for a well managed planet to support our existing population, but may impact other life on the planet.

So the answer is not clear, but there are errors in the calculation. Note that 25 mile square (25 mi X 25 mi) is not the same as 25 square miles (25 sq mi).