population density

population density, the number of individuals of a certain species per unit area. It can be expressed by the formula $D_{\mathrm{p}}=N_{\mathrm{i}}/A$ where D_p is population density, N_i is the number of individuals of the species in question, and A is the area expressed in square units, often square kilometers (km²) or square miles (miles²). When analyzing human populations, the related measures of agricultural density and physiological density are often preferred. Agricultural density is the number of farmers per unit of arable land and is used to study the productivity of farms. Physiological density is the number of individuals per unit of arable land and is used to examine how many people a unit of agricultural land supports.

Uses

In the sciences

Population density is used in a variety of ways in the social and biological sciences. In the social sciences population density is concerned with the number of humans who lived or are living in a certain area. It is frequently used in studies of urbanization, which may consider data from time periods ranging from the urban revolution to modernization. The population density of human settlements is also used in studies of infectious disease and how environmental factors affect its spread among people as well as in studies that track the impact of crowded or sparse environments on mental health.

More From Britannica

population ecology: Population density and growth

Ecologists use population density as part of population ecology, which studies the distribution and abundance of animal and plant populations. Both low and high population densities can present challenges for a species. Increased competition for food, predation, migration, and disease are common in areas with high population densities. However, in areas where a species has a low population density, individuals may struggle to find mates. Population density is also used to calculate carrying capacity.

Problems in population density

Population density is an imperfect measure. It can obscure differences in settlement intensity within a unit of land. If, for example, an area of land contains both city and countryside and a simple population density is calculated, those who live in the city will appear to live in a lower-density area than they actually do, while those in towns and villages will appear to live in a higher-density area. Population-weighted densities, which weight different densities by their population sizes, can be used to counter this distortion. Censuses and other measures of population may struggle to accurately count certain populations, particularly mobile populations such as nomadic groups, migrants, and refugees. Individuals without housing and those who live in settlements that are not recognized by governmental authorities are often undercounted as well. Some studies that consider population density, particularly those focusing on animals, use sampling to estimate the number of individuals in the area of interest and so are subject to sampling error, which happens because samples contain only a fraction of values in a population and are thus not perfectly representative of the entire set.

Examples

The table below demonstrates the calculation of the population density for a sample of 10 regions.