Population, Migration and Urbanization
Measuring population
A census counts everyone at a point in time; a survey samples. Know birth and death rates (per 1,000), rate of natural increase (births minus deaths), net migration, population growth rate, doubling time (about 70 ÷ annual growth per cent), population density (people per square kilometre), age–sex structure shown in population pyramids, dependency ratio, life expectancy, infant mortality and fertility rate.
Change and movement
The demographic transition model runs from high birth and death rates, through falling death rates and rapid growth, to falling birth rates and low, stable rates with an ageing population. Migration involves push and pull factors; internal or international; voluntary or forced. A refugee crosses a border and is protected under international law; an internally displaced person does not cross one. Urbanisation brings rural–urban drift, urban growth, primacy of one city, informal settlements, and pressure on housing, water and waste; counter-urbanisation and remittances also matter.
Traps
Density is not overpopulation - a crowded city can be well served while an empty region is poor. Growth rate and absolute increase are different. Migration is the movement; immigration and emigration are directions. A young population means high child dependency now; an ageing one means high old-age dependency later.
Worked example
A country has 4,000 people aged 0–14, 5,500 aged 15–64 and 500 aged 65+. Dependency ratio = (4,000 + 500) ÷ 5,500 × 100 = 81.8, meaning about 82 dependants per 100 workers - a heavy load on schools, clinics and wages.