World geography: population and migration (grade 9)

A population pyramid is a bar graph of a country's people by age. The youngest are at the bottom and the oldest at the top. A wide base means many children, which comes from a high birth rate.

A pyramid that is narrow at the bottom and wide near the top shows an aging country with few births. Fewer workers must support more retirees who need pensions and health care.

A country with too few workers can wait for babies to grow up, which takes about 20 years. Or it can admit adult immigrants, who can start working right away.

A push factor drives people away from home, like drought, war, or lack of jobs. A pull factor draws them toward a new place, like jobs, safety, or family.

A refugee is forced to flee war or persecution across a border. People forced to move inside their own country are called internally displaced. People who move mainly for better work are economic migrants.

Migration often happens as a chain. One person moves, then sends money and news home. Relatives and friends follow, and a neighborhood of people from one region grows. The money migrants send home is called remittances. It raises family incomes and can be a large part of some countries' economies.

Population density is people per square mile. Measuring per square mile of farmland can tell a different story. Most of Egypt is desert, so its people crowd along the narrow Nile Valley and Delta. Density per farmland is very high even though density per total land is modest.

Urbanization is a growing share of people living in towns and cities. A country's total population can stay the same while its cities fill up, because people move from the countryside.