Population density

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Image:World population density map.PNG
Population density by country, 2006

Population density is a measurement of population per unit area or unit volume. It is frequently applied to living organisms, humans in particular.

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[edit] Biological population densities

Population density is a common biological measurement and is often used by conservationists as a more appropriate measure than population size.

Low densities may cause an extinction vortex and lead to further reduced fertility. This is called the Allee effect, after W. C. Allee who first identified it. Examples of the its causes in low population densities include:

  • Increased problems with locating mates
  • Increased inbreeding
  • Increased susceptibility to catastrophic events

Different species have different expected densities. R-selected species commonly have high population densities, while K-selected species may have lower densities. Low densities may be associated with specialised mate location adaptations such as specialised pollinators; as found in the orchid family (Orchidaceae).

[edit] Human population density

Image:Crowd in HK.JPG
A street in Hong Kong, one of the most densely-populated places in the world.

For humans, population density is the number of persons per unit of area (which may include or exclude cultivated or potentially productive area). Commonly this may be calculated for a county, city, country, another territory, or the entire world.

The world population is 6.5 billion humans, and Earth's area is 510 million square kilometers (200 million square miles). Therefore the world-wide human population density is 6.5 billion / 510 million = 13 per km² (33 per sq mi), or 43 per km² (112 per sq mi) considering that humans live on land, which forms 150 million km² (58 million sq mi) of the earth. This density rises with the population growth, and some people think there is a limit of what the Earth can support.

Several of the highest-density territories in the world are very small city-states, micronations or dependencies. These territories share a relatively small area and an exceptionally 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 exceptionally high population densities are often considered to be overpopulated, though the extent to which this is the case depends on factors like quality of housing and infrastructure or access to resources. Most of the largest densely-populated cities are in southern and eastern Asia, though Cairo and Lagos in Africa also fall into the category. City population is however, heavily dependent on the definition used for the urban area: densities will be far higher for the central municipality than when more recently-developed and as yet administratively unincorporated suburbs are included, as in the concepts of agglomeration or metropolitan area, the latter including sometimes neighbouring cities.

[edit] Other methods of measuring population density

Image:Pop density.jpg
Population density map of the world in 1994.

While the arithmetic density is the most common way of measuring population density, several other methods have been developed which aim 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 km² or mi².

Physiological density – The total population divided by the amount of arable land.

Agricultural density – The total rural population to the amount of agricultural land.

Residential density – The number of people living in an urban area divided by the amount of residential land.

Ecological optimum – The density of population which can be supported by the area's natural resources.

[edit] See also

Residential density – The number of people living in an urban area divided by the amount of residential land.

Ecological optimum – The density of population which can be supported by the area's natural resources.

[edit] External links

als:Bevölkerungsdichte an:Densidá de poblazión ast:Densidá de población zh-min-nan:Jîn-kháu bi̍t-tō͘ be:Шчыльнасьць насельніцтва bs:Gustoća stanovništva bg:Гъстота на населението ca:Densitat de població cs:Hustota zalidnění cy:Dwysedd poblogaeth da:Befolkningstæthed de:Bevölkerungsdichte el:Πυκνότητα πληθυσμού es:Densidad de población eo:Loĝdenso fr:Densité de population gl:Densidade de poboación ko:인구 밀도 hr:Gustoća stanovništva ilo:Densidad ti populasion id:Kepadatan is:Þéttleiki byggðar it:Densità di popolazione he:צפיפות אוכלוסייה ka:მოსახლეობის სიმჭიდროვე la:Spissitudo incolarum lv:Iedzīvotāju blīvums lt:Gyventojų tankis li:Bevoukingsdeechde hu:Népsűrűség mk:Густина на населеност ms:Kepadatan mo:Денситатя популацией nl:Bevolkingsdichtheid nds-nl:Bevolkingsdichheid ja:人口密度 no:Befolkningstetthet nn:Folketettleik oc:Densitat de populacion km:ដង់ស៊ីតេ​ប្រជាជន nds:Inwahnerdicht pl:Gęstość zaludnienia pt:Densidade populacional ro:Densitatea populaţiei rmy:Butvaripen le manushengo ru:Плотность населения simple:Population density sk:Hustota obyvateľstva sl:Gostota prebivalstva sr:Густина насељености sh:Gustoća stanovništva fi:Väestötiheys sv:Befolkningstäthet ta:மக்கள்தொகை அடர்த்தி th:ความหนาแน่นประชากร vi:Mật độ dân số udm:Улӥсьёслэн плотностьсы uk:Щільність населення vls:Bevolkiengsdichtheid zh:人口密度

Population density

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