I think the lesson here is that 500 people per square mile is a very unnatural density- the largest-lot subdivisions will be higher, anything purely rural (even including hamlets, and in wet climates) will be lower. You need a hodgepodge to hit that mark.
If you get fine-grained enough, down to the block, 500 people per square mile is too low I think. But at a township level it's more defensible.
If you tell people from China and India that 501 people per square mile can't be rural, they will laugh at you.
