[[File:Population density countries 2017 world map, people km.svg|450px|thumb|Population density (people per km 2 ) by country, 201 by population density.svg|450px|thumb|Population density (people per km 2 ) [[File:Wor density 1994 - with equatorg|thumb|450px|Population density (people per km 2 ) map of the world in 1994. In relation to the equator it is seen that the vast majority of the human population lives in the Northern Hemisphere .]]

Population density (in agriculture : standing stock and standing crop ) is a measurement of population per unit area or unit volume; it is a quantity of type number density . It is frequently applied to living organisms , and most of the time to humans . It is a key geographical term. [26]

## Biological population densities

Population density is population divided by total land area or water volume, as appropriate. [26]

Low densities may cause an extinction vortex and lead to further reduced fertility. This is called the Allee effect after the scientist who identified it. Examples of the causes in low population densities include: [3]

• Increased problems with locating sexual mates
• Increased inbreeding

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 7,500,000,000 [15] and Earth 's total area (including land and water) is 510,000,000 square kilometers (197,000,000 sq. mi.). [2] Therefore, the worldwide human population density is around 7,500,000,000 ÷ 510,000,000 = 14.7 per km 2 (38 per sq. mi). If only the Earth's land area of 150,000,000 km 2 (58,000,000 sq. mi.) is taken into account, then human population density increases to 50 per km 2 (129 per sq. mile). This includes all continental and island land area, including Antarctica . If Antarctica is also excluded, then population density rises to over 55 people per km 2 (over 142 per sq. mile). [26] However, over half 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 . 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 Southeast 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 almost invariably higher for the central city area than when suburban settlements and the intervening rural areas are included, as in the areas of agglomeration or metropolitan area , the latter sometimes including 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.

### By political boundaries

With population above 1,000,000
Rank Country/Region Population Area (km 2 ) Density
(Pop. per km 2 )
1
5,535,00071976982 Hong Kong 7,234,8001,10465533 1,816,37936050454 Bahrain 1,404,90075018735 Bangladesh 161,609,000147,57010956 Taiwan 23,361,14736,1906467 Mauritius 1,288,0002,0406318 Lebanon 6,237,73810,4525979 South Korea 51,529,33899,72051710 Rwanda 11,262,56426,338428
With population above 10,000,000
Rank Country/Region Population Area (km 2 ) Density
(Pop. per km 2 )
2 Taiwan (R.O.C) 23,361,147 36,190 646
3 South Korea 51,529,338 99,720 517
4 Rwanda 11,262,564 26,338 428
5 Netherlands 17,071,100 41,526 411
6 India 1,326,801,576 3,287,263 404
7 Haiti 10,413,211 27,750 375
8 Belgium 11,239,755 30,528 368
9 Burundi 10,114,505 27,834 363
10 Philippines 102,078,300 300,076 340

### Other methods of measurement

Although arithmetic density is the most common way of measuring population density, several other methods have been developed to provide a more accurate measure of population density over a specific area.

• Arithmetic density : The total number of people / area of land (measured in square miles or square kilometers)
• Physiological density : The total population / area of arable land
• Agricultural density : The total rural population / area of arable land
• Residential density : The number of people living in an urban area / area of residential land
• Urban density : The number of people inhabiting an urban area / total area of urban land
• Ecological optimum : The density of population that can be supported by the natural resources