Age Structure Diagrams
Introduced| English |
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| age structure diagram/eɪdʒ ˈstrʌktʃə ˈdaɪəɡræm/ |
A population's snapshot
- To predict a country's future, look at its ages today.
- A population full of children will grow; one full of elderly will shrink.
- An age structure diagram shows this at a glance.
- Its shape is a powerful forecasting tool.
What the diagram shows
- An age structure diagram 年龄结构图 stacks age groups from youngest at the bottom to oldest at the top.
- Males are shown on one side, females on the other.
- Wide bars mean many people in that age group.
- The overall shape reveals whether the population is young or old.
An age structure diagram shows…
An age structure diagram shows the number of males and females in each age group.
A wide base means growth
- A wide base means many children and young adults.
- These young people are the parents of the future.
- So a wide-based, pyramid-shaped diagram predicts rapid growth.
- Many developing countries have this shape.
A wide base (many young people) predicts a population that will…
Many young people means many future parents, so the population will grow.
A narrow base, with few children and many elderly, predicts a ____ population.
Few young people means few future parents, so the population will shrink.
Narrow base means decline
- A narrow base means few children compared with older people.
- Fewer future parents means the population will shrink.
- A top-heavy diagram, with more elderly than young, predicts decline.
- A roughly straight-sided shape predicts a stable population.
What does the shape predict?
Sort each age structure shape by whether the population will grow, stay stable, or shrink.
The shape of an age structure diagram helps predict future population change.
The proportion of young to old predicts whether the population will grow or shrink.
Select all true statements about age structure diagrams.
The shape predicts a great deal about future population change. The other three are correct.
The base of the diagram — the number of children — is what predicts the future. A wide base guarantees growth for decades, even if birth rates fall today, because so many future parents are already born. This built-in momentum is why fast-growing populations are hard to slow quickly.
Two countries compared:
- Country A has a wide-based pyramid: half its people are under 15, so it will grow fast for decades.
- Country B has a narrow base and many elderly: its population will shrink and age.
- The same total population, but two very different futures — read straight from the diagram's shape.
An age structure diagram shows the number of people in each age group. A wide base (many children) predicts a growing population; a narrow base (few children) predicts a shrinking one; a straight-sided shape predicts stability. The shape forecasts future population change.