We live in a world with more than 159 million km^2 of land. So why is it that more than half of the world's population lives on 5% of the land, and 90% of the world's population on less then 20% of the land? What 20% of the land do humans occupy?
**Arithmetic (crude) density is the total number of people divided by the total land area and is the measure most often used by geographers. So if the world has approximately 7 billion people divided by 159M km^2 of land, then the crude density of Earth is 44.03 people/km^2. So why is it that Shang Hai (the world's densest population) has a population density of 6,845 people/km^2, 156 times the crude density of earth's population?
By 2030 more than 6 in every 10 people on earth will live in **Urban areas (cities). Since the very beginning of human settlement (the first agricultural revolution), humans have congregated near water. Throughout history this trend continued. This is most likely not sole attributable to agriculture, but trade and transportation as well. Even now, humans tend to live near people who share cultural characteristics, be it ethnicities, language, religion or any other unifying factor. The primary movement of humans was most often driven by the desire for economic gain. Consider the **interregional movement of the Mongols throughout South East Asia, Eastern Europe, and the Middle east, in each new area that they settled, The primary resource that they tapped into was access to the economy and control of