Population density refers to where people shop settlement patterns the number of people who live in a square mile or kilometer explains why people in a region live where they do

Population density is the study of how many people live in some area as compared to other areas - this helps for example predict whether the area can preduce enough food for itself. It is measured in the number of people per a unit of area.

The correct answer then is:
the number of people who live in a square mile or kilometer 

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