There are 7.1 billion people. New Zealand’s area is 103,738 square miles.
Manhattan’s population density is 70,517 people per square mile.
7,100,000,000 people / 103,738 sq mi in New Zealand = a density of 68,441 people/sq mi. It would actually be less dense than Manhattan.
This is crazy because walking around Manhattan, it doesn’t feel that dense. And what you feel when you walk around Manhattan includes all the tourists and work commuters who don’t live there (which makes the actual people density of Manhattan much higher than 70,517 people/sq mi). So our hypothetical New Zealand would feel far emptier than Manhattan on a Wednesday, and all people would be there.
Not sure what the takeaway is—clearly what it’s not is “Wow so over-population isn’t a problem,” because that’s much more related to resources than land space. But it’s cool to think about.
Much more on this topic here.