A square mile = 27,878,400 square feet
A square mile also = 640 acres.
31,580/.75 = 43,440 persons per square mile
That is 27,878,400/43,440 = ~642 square feet per person so each person has a square approximately 25 feet on each side.
43440/640 = ~ 68 people per acre
This is a fairly dense population density by US standards. Of course if housing were constructed in high rise structures located on a couple of acres, there would be a comfortable area of open space.
