A population is a subgroup of individuals within the same species that are living and breeding within a geographic area. The number of individuals living within that specific location determines the population density, or the number of individuals divided by the size of the area.

Population density can be used to describe the location, growth, and migration of many organisms. In the case of humans, population density is often discussed in relation to urbanization, immigration, and population demographics.

Globally, statistics related to population density are tracked by the United Nations Statistics Division, and the United States Constitution requires population data to be collected every 10 years, an operation carried out by the U.S. Census Bureau. However, data on human population density at the country level, and even at regional levels, may not be very informative; society tends to form clusters that can be surrounded by sparsely inhabited areas. Therefore, the most useful data describes smaller, more discrete population centers.

Dense population clusters generally coincide with geographical locations often referred to as city, or as an urban or metropolitan area; sparsely populated areas are often referred to as rural. These terms do not have globally agreed upon definitions, but they are useful in general discussions about population density and geographic location.

Population density data can be important for many related studies, including studies of ecosystems and improvements to human health and infrastructure. For example, the World Health Organization, the U.S. Energy Information Administration, the U.S. Global Change Research Program, and the U.S. Departments of Energy and Agriculture all use population data from the U.S. Census or UN statistics to understand and better predict resource use and health trends.

Key areas of study include the following:

  • Ecology: how increasing population density in certain areas impacts biodiversity and use of natural resources.
  • Epidemiology: how densely populated areas differ with respect to incidence, prevalence, and transmission of infectious disease.
  • Infrastructure: how population density drives specific requirements for energy use and the transport of goods.

This list is not inclusive—the way society structures its living spaces affects many other fields of study as well. Scientists have even studied how happiness correlates with population density. A substantial area of study, however, focuses on demographics of populations as they relate to density. Areas of demographic breakdown and study include, but are not limited to:

  • age (including tracking of elderly population centers);
  • sex (biological classification as male or female); and
  • race and ethnic group, or cultural characteristics (ethnic origin and language use).

Population Density

Studies of human populations often happen at or below the city level in places like Manhattan, which is part of New York City, New York, United States.


to produce offspring.


program of a nation, state, or other region that counts the population and usually gives its characteristics, such as age and gender.

cultural characteristic

feature of an area or population that identifies it. Cultural characteristics are often defined as food, language, art, clothing, religion and holidays.


having to do with the social characteristics and statistics of a population.


community and interactions of living and nonliving things in an area.

ethnic group

people sharing genetic characteristics, culture, language, religion or history.


structures and facilities necessary for the functioning of a society, such as roads.


to live in a specific place.


movement of a group of people or animals from one place to another.

natural resource

a material that humans take from the natural environment to survive, to satisfy their needs, or to trade with others.


living or once-living thing.


total number of people or organisms in a particular area.


arbitrary grouping of people based on genetics and physical characteristics.


any area on Earth with one or more common characteristics. Regions are the basic units of geography.


substances such as water, air, shelter, and food sources which are valuable in supporting life.


male or female: division into which sexually reproducing organisms are divided.


the collection and analysis of sets of numbers.


process in which there is an increase in the number of people living and working in a city or metropolitan area.