Counting people and tracking how populations change is the work of demography. The field examines births, deaths, migration, and the resulting age and sex structure of populations. Governments rely on demographic data for planning schools, hospitals, and pensions.

Fertility rates, life expectancy, and net migration determine whether a population grows, shrinks, or ages. The demographic transition model describes the historical shift from high birth and death rates to low ones as societies industrialize. Population pyramids visualize the age structure at a glance.

Demographers use censuses, surveys, and vital registration systems. Their projections help anticipate future demand for housing, jobs, and services. In an era of rapid urbanization and uneven global growth, demographic analysis remains essential for public policy.

• Statistical study of human populations
• Tracks births, deaths, and migration
• Uses censuses and population pyramids
• Informs planning and policy decisions