6.1 Measuring population
Birth and death rates are usually given per thousand people (‰). The rate of natural increase is the birth rate minus the death rate: births 15‰ and deaths 6‰ give natural increase of 9‰, or 0.9%. Adding migration in and out gives the total population change. The fertility rate is the average number of children a woman has in her lifetime; about 2.1 is needed for a population to replace itself.
The "rule of 70" estimates how long a population growing at a steady rate takes to double: divide 70 by the growth rate in percent. The dependency ratio is the number of children (0–14) and older people (65+) for every 100 people of working age (15–64); it shows the burden the economy carries.
FormulaNatural increase (‰) = birth rate − death rate · Doubling time ≈ 70 ÷ growth rate (%) · Dependency ratio = (0–14 + 65+) ÷ (15–64) × 100 · Arithmetic density = population ÷ area
6.2 Demographic transition and pyramids
The demographic transition model describes the stages countries pass through as they develop. In stage 1, birth and death rates are both high and the population grows slowly. In stage 2, health and nutrition improve, deaths fall fast but births stay high: a population explosion. In stage 3, urbanisation, education for women and their entry into work bring births down too. In stage 4, both are low and the population levels off. Some countries have entered stage 5, where births fall below deaths and the population shrinks.
A population pyramid shows the age and sex structure. A wide-based, triangular pyramid shows high fertility and a young population (stage 2); straight sides show a stable population; a narrowing base with a wide middle and top shows an ageing population. Türkiye's population is about 85.7 million (2024). Its fertility rate has fallen to about 1.5, so the population is ageing quickly and the base of its pyramid is narrowing.
6.3 Migration and urbanisation
Migration results from push and pull factors. Lack of work, farm mechanisation, drought or war push people away; jobs, education and health services pull them to cities. In Türkiye, farm mechanisation and industrial growth after the 1950s started a huge rural-to-urban migration; today the large majority of people live in cities.
Rapid urbanisation can bring unplanned building, traffic, air pollution and housing and infrastructure problems. A city that holds a very large share of a country's population and economy is a "primate city"; Istanbul is the example in Türkiye. Urban planning, public transport and earthquake-safe renewal are keys to sustainable cities.
Key terms
- Natural increase
- The difference between the birth rate and the death rate.
- Fertility rate
- The average number of children a woman has in her lifetime.
- Dependency ratio
- Children and older people per 100 people of working age.
- Primate city
- A city holding a very large share of a country's population and economy.
End-of-unit problems
Solve each one yourself first, then open the solution.
In a country the birth rate is 24‰ and the death rate 7‰, with no migration. What is the rate of natural increase in percent? Roughly how many years will the population take to double?
Show the solution
Natural increase = 24 − 7 = 17‰ = 1.7%. Doubling time ≈ 70 ÷ 1.7 ≈ 41 years.
A country has 18 million people aged 0–14, 58 million aged 15–64 and 9 million aged 65+. Find the dependency ratio. If fertility keeps falling, which part of the ratio will grow in 30 years?
Show the solution
(18 + 9) ÷ 58 × 100 ≈ 46.6, so about 47 dependants for every 100 people of working age. As fertility falls the child share shrinks, but as today's large working generations grow old, old-age dependency (65+) rises sharply.
Which stage of the demographic transition does a pyramid with a very wide base that narrows quickly upwards show? Name two challenges this country will face in the next 20 years.
Show the solution
Stage 2 (or early stage 3): high fertility, falling death rates, a young and fast-growing population. Challenges: schools and teachers for many children; and, in 15–20 years, creating enough jobs for the large generation entering the workforce (plus demand for housing, food and health care).
Calculate the arithmetic population density of a country with an area of 780,000 km² and a population of 85.7 million. Why might this figure be misleading about how people are actually spread?
Show the solution
85,700,000 ÷ 780,000 ≈ 110 people/km². It is an average: people crowd onto coasts, plains and big cities, while mountainous, dry and cold areas are sparsely populated. Physiological density (people per area of farmland) or regional densities give a more realistic picture.