"Population density is an often reported and commonly compared statistic for places around the world. Population density is the measure of the number per unit area. It is commonly represented as people per square mile (or square kilometer), which is derived simply by dividing total area population / land area in square miles (or square kilometers)."
Example of Low Population Density
"As an example of the low population density in the West, I often like to cite Idaho County, Idaho: This one county measures 8,485 square miles-bigger than Connecticut and Rhode Island combined. But it has a population] of just 15,400. And of those residents, roughly 3,300 people live in Grangeville, the county seat. Who lives in the rest of the county? Nary a soul. There are far more deer and elk than there are people. The population density of the county is 1.8 people per square mile. The county has more than 3 million acres of U.S. Forest Service land, BLM land, and designated federal wilderness areas. Now that is elbowroom!"  
- Rawles, James Wesley. Rawles on Retreats and Relocation. 1st. Clearwater, Idaho: The Clearwater Press, 2007. p. 10. Print.
- http://www.survivalblog.com/retreatareas.html Recommended Retreat Areas accessed January 22, 2014