Population growth, change and density

Last time

Before we start: last time, in Plate tectonics, earthquakes and volcanoes, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

More people, or fewer

Some countries' populations grow fast, while others are shrinking. The reasons are births, deaths and migration. This lesson covers population change, the demographic transition, population structure, and population density.

Population change

Natural increase is the birth rate minus the death rate, usually given per thousand people per year. Migration also changes population: immigration adds people, emigration removes them. Countries such as Niger have very high growth; others, such as Spain, have low or negative natural increase.

Why birth rates differ

High birth rates: children work on farms and support parents in old age; high infant mortality; little access to contraception; early marriage. Low birth rates: women in education and careers, the high cost of raising children, and widely available contraception. Government policies, such as China's former one-child policy, can also change birth rates.

Why death rates fall

Better health care, vaccinations, clean water, sanitation and food reduce death rates. Death rates can rise with war, disease outbreaks, famine, and an ageing population. Life expectancy rises as death rates fall.

The demographic transition model

The demographic transition model shows how birth and death rates change as a country develops. In stage 1 both are high. In stage 2 the death rate falls fast, so population grows quickly. In stage 3 the birth rate falls. In stage 4 both are low. In stage 5 the birth rate may fall below the death rate. Niger is in stage 2; Spain is in stage 4 or 5.

Population structure

A population pyramid shows the population by age and sex. A wide base shows a high birth rate and many young dependants, typical of poorer countries. A narrow base and wide top show an ageing population, typical of richer countries, with many elderly dependants.

Over- and under-population

Over-population is when there are too many people for the resources available, leading to poverty and shortages. Under-population is when there are too few people to use the resources fully. Optimum population is the best balance for a high standard of living.

Population density

Population density is the number of people per square kilometre: total population divided by area. Dense areas: flat, fertile land, a mild climate, water, and jobs, such as river valleys and cities. Sparse areas: mountains, deserts, very cold or very wet regions, and remote areas.

Calculating density

If a country has 10 million people in an area of 50,000 square kilometres, its density is 10 million divided by 50,000. That is 200 people per square kilometre. Always give the unit: people per square kilometre.

Mistakes that lose marks

Mistake one: forgetting migration when explaining population change. Mistake two: giving density without units. Mistake three: describing a pyramid without linking it to birth and death rates. The fix: births, deaths, migration, and units.

The full-marks tip

The full-marks tip: explain change with births, deaths and migration, using the demographic transition model. Calculate density as population divided by area, with the unit.

On one card

So, on one card: population. Keep it for revision.