Population

Population is the number of individuals in a specified area or group. In human demography, it usually refers to the total number of people in a country, region, or city, and is described by size, density, and distribution. Key structural characteristics include age composition, sex ratio, and geographic pattern of settlement.

Population change results from births, deaths, and net migration. Fertility levels influence future size; mortality affects survival; migration reshapes spatial distribution. Other important indicators include the dependency ratio and median age.

Measurement relies on censuses, vital statistics, and surveys, often supplemented by population registers and administrative data. Projections use demographic methods, such as the cohort-component model, to estimate future size and structure, with uncertainty stemming from fertility, mortality, and migration assumptions.

Global patterns show substantial variation; many countries are experiencing aging populations and urbanization. Population size interacts with resources, economy, health, and environment, influencing policy decisions in areas such as education, housing, labor markets, and social protection.