one person: 2 ft wide by 1.5 ft deep

6 billion people: 12 billion ft wide by 1.5 ft deep

or 18 billion square ft

one square mile: 5280 ft by 5280 ft

or 27,878,400 square ft

18 billion square ft: 646 square miles

646 square miles: 20 miles by 33 miles

All the people in the world can stand side by side, front to back in an area of 20 miles by 33 miles.