We can find the answer by dividing the world population by the area of NYC in square feet.
There is 27,878,400 sq ft in a mile because 5280^2 is that value. So that means
7400000000 people in 27,878,400 sq ft. You can divide that into sqft/person which is 0.00376 sqft/person. Now multiply that by 305. you will get 1.149 sq/person in NYC.
Hope this helps!
ps that was a crazy problem