Population pyramid – three shapes and forecasting by birth and death rates
GeographyPopulation & SettlementAges 15–16
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Population & Settlement
A population pyramid by 5-year age group (male on the left, female on the right) shows three shapes: expansive (wide base, young population, fast growth), stationary (even sides, slow growth) and constrictive (narrow base, aging population, decline). Drag the birth-rate and death-rate sliders, then press Run: population is forecast year by year with the cohort-component method (births enter the 0–4 group, deaths applied by age, survivors move up a group), and the pyramid gradually changes shape while total population, natural increase rate, the share of three age groups and the current pyramid type are shown.
Lesson: Population size, population growth and age–sex structure (population pyramid)
What it shows
A population pyramid shows the share of males and females in each 5-year age group. An expansive pyramid with a wide base means many children and fast growth; a stationary pyramid means slow growth; a constrictive pyramid with a narrow base signals an ageing, often shrinking population. The natural increase rate in per cent is (crude birth rate − crude death rate) / 10, with both rates in ‰. The model projects the population year by year: births enter the 0–4 group, deaths are applied by age and survivors move up.
How to use
Choose Expansive, Stationary or Constrictive as the starting shape, set the Crude birth rate and Crude death rate sliders, and press Run forecast. Watch the base and top of the pyramid, the total population and the pyramid type as the years pass. Try a sharp fall in the birth rate on an expansive pyramid and see how long it takes to age. Turn on Color three age groups to follow the 0–14, 15–64 and 65+ shares.
Parameters you can change
- Initial pyramid shape Expansive (young population), Stationary, Constrictive (aging population)
- Crude birth rate 5–50 ‰
- Crude death rate 3–30 ‰
- Forecast years 5–100 years
- Simulation speed 0.5–10 years/second
- Color three age groups (0–14, 15–64, 65+)
Questions to explore
- With a birth rate of 30‰ and a death rate of 10‰, what is the natural increase rate?
- If the birth rate equals the death rate, how does the pyramid's shape change over several decades?
- After a sharp fall in the birth rate, how many years pass before the 65+ share reaches 14%?
