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For humans, population density is the number of people per unit of area, usually quoted per square kilometer or square mile (which may include or exclude, for example, areas of water or glaciers). Commonly this may be calculated for a county, city, country, another territory, or the entire world. The world's population is around 7 billion,[3] and Earth's total area (including land and water) is 510 million square kilometers (197 million square miles).[4] Therefore the worldwide human population density is around 7 billion ÷ 510 million = 13.7 per km2 (35 per sq. mile). If only the Earth's land area of 150 million km2 (58 million sq. miles) is taken into account, then human population density increases to 47 per km2 (120 per sq. mile). This includes all continental and island land area, including Antarctica. If Antarctica is also excluded, then population density rises to over 50 people per km2 (over 130 per sq. mile).[1] However over half[citation needed] of the Earth's land mass consists of areas inhospitable to human habitation, such as deserts and high mountains, and population tends to cluster around seaports and fresh water sources. Thus this number by itself does not give any helpful measurement of human population density. Several of the most densely populated territories in the world are city-states, microstates, and dependencies.[5][6] These territories have a relatively small area and a high urbanization level, with an economically specialized city population drawing also on rural resources outside the area, illustrating the difference between high population density and overpopulation. Cities with high population densities are, by some, considered to be overpopulated, though this will depend on factors like quality of housing and infrastructure and access to resources.[7] Most of the most densely populated cities are in southern and eastern Asia, though Cairo and Lagos in Africa also fall into this category.[8] City population and especially area are, however, heavily dependent on the definition of "urban area" used: densities are amost invariably higher for the central city area than when suburban settlements and the intervening rural areas are included, as in the concepts of agglomeration or metropolitan area, the latter including sometimes neighboring cities. For instance, Milwaukee has a greater population density when just the inner city is measured, and the surrounding suburbs excluded.[9] In comparison, based on a world population of seven billion, the world's inhabitants, as a loose crowd taking up ten square feet (one square metre) per person (Jacobs Method), would occupy a space a little larger than Delaware's land area. |
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