Key Idea: Topic 1.2 is about how populations change and how that movement reshapes places. It pulls together four ideas: 1.2.1 — population structure: reading a population pyramid for a country's age and sex make-up, plus natural increase and the sex ratio. 1.2.2 — megacities: what a megacity is (10 million+) and the drawbacks and benefits of cities growing very fast, felt by individuals and wider society. 1.2.3 — forced migration: people driven from home with no real choice — by political, environmental, social or developmental causes — becoming refugees or internally displaced. 1.2.4 — voluntary internal migration: people choosing to move within their country, changing both the source they leave and the destination they reach. This is core content, examined on Paper 2 — a data-response read off a population pyramid, line graph or map, a short structured Explain, and it can feed the extended-response essay.
👥 1.2.1 — Population structure: pyramids, age & sex
A population pyramid shows a country's age and sex structure — males on the left, females on the right, youngest at the bottom, with bar length = the share in each group. The shape tells the story, and the skill examiners test is reading the bars (a figure) then describing the shape, with no reasons for a Describe command.
Read both the bars (values) and the overall shape — both are tested.
🔒 Interactive diagram
Explore the labelled diagram, charts and maps for this topic in study mode.
Pyramid shape → what it tells you
| Shape | What it means |
|---|---|
| Wide base, narrows quickly | Youthful — high birth rate, fast growth (often lower-income) |
| Narrow base, wide middle/top | Ageing — low birth rate, more elderly (often higher-income) |
| A bulge in one band | A past baby boom, or in-migration of working-age people |
| Longer female side at the top | Women tend to live longer — common in the oldest groups |
Key terms — structure
- Population pyramid — a chart of a country's age and sex structure.
- Age structure — how the population splits between young, working-age and old.
- Dependency ratio — the non-working (under-15s + over-65s) compared with the working-age (15–64) population.
- Sex ratio — the balance of males to females (often per 100 females).
- Rate of natural increase — births − deaths (per 1000 per year), excluding migration.
🏙️ 1.2.2 — Megacities & the consequences of rapid growth
A megacity has 10 million or more inhabitants. Most are in lower- and middle-income countries, mainly in Asia and Africa, where cities grow fastest. Rapid growth has two sides — drawbacks and benefits — and a strong answer names who feels each: an individual (one resident) or wider society (the whole city or country).
Rapid megacity growth — two sides
| Drawbacks (problems) | Benefits (opportunities) |
|---|---|
| Housing shortages and informal settlements (slums) | More, better-paid jobs than in rural areas |
| Traffic congestion and air pollution | Schools, hospitals and services within reach |
| Pressure on water, sanitation and electricity | Economic growth — megacities drive national GDP |
| Unemployment and inequality | Cheaper to serve people living close together |
Key terms — megacities
- Megacity — an urban area of 10 million or more people.
- Urbanisation — the rising share of people living in towns and cities.
- Rapid urban growth — a city's population rising quickly, from migration and natural increase.
- Informal settlement — unplanned, often self-built housing (a slum) that grows when a city expands faster than it can house people.
🚨 1.2.3 — Forced migration & displacement
Forced migration is movement people have no real choice about — they are pushed out by danger or disaster, not pulled by opportunity. Forced migrants who cross an international border become refugees; those forced to flee but who stay inside their own country are internally displaced persons (IDPs). An Explain answer must name the cause and the mechanism that forces the move.
Causes that force people to move
| Type of cause | Example mechanism |
|---|---|
| Political | Armed conflict or persecution → homes destroyed, lives at risk → people flee for safety |
| Environmental | Drought, flooding or sea-level rise → crops fail, land lost → people leave to survive |
| Social | Ethnic or religious persecution of a group → members flee to avoid harm |
| Developmental | A dam or mine floods or seizes land → residents are evicted and relocated |
Key terms + named cases
- Forced migration — movement people are compelled to make by a threat to life or livelihood.
- Refugee — a forced migrant who has crossed an international border.
- Internally displaced person (IDP) — forced to flee but still inside their own country.
- Push factor — a negative condition (war, drought) that drives people away.
- Named cases — Syria (conflict, 6 million+ refugees), Lake Chad (drought + conflict), Three Gorges Dam (developmental, 1 million+ relocated).
🧳 1.2.4 — Voluntary internal migration & place change
Voluntary internal migration is choosing to move home within your own country — usually from low-opportunity source areas to high-opportunity destinations (often big cities). It changes both places, and the effects are usually opposite: the source is left ageing and hollowed-out, while the destination gains workers but faces pressure on housing and services. Because young workers concentrate in a few places, it can even hold back national development.
Place change — source vs destination
| Source area (people leave) | Destination area (people arrive) |
|---|---|
| Ageing, shrinking community — young people gone | Younger, growing population |
| Schools and clubs close; a 'hollowed-out' place | Pressure on housing, schools and hospitals |
| Smaller workforce, businesses closing, prices fall | More workers, but rising house prices and congestion |
| Push factors: few jobs, low pay, poor services | Pull factors: more jobs, higher wages, better services |
Key terms — internal migration
- Internal migration — moving home but staying inside the same country (no border crossed).
- Voluntary — the migrant chooses to move; it is not forced by war, disaster or eviction.
- Source / destination area — the place migrants leave / the place they move to.
- Push / pull factors — what drives people from the source / draws them to the destination.
- Net migration — arrivals minus departures; positive = a place gains people, negative = it loses them.
✍️ IB-style questions
Explain two reasons why a country with a wide-based population pyramid may experience rapid urban growth.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Examine the view that the changes brought by migration harm the places people leave more than they benefit the places people move to.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
✅ Quick self-check
Tap each card to reveal the answer.
What does a wide-based pyramid tell you, and what is natural increase? A wide base = a youthful population, high birth rate, fast growth. Natural increase = births − deaths (per 1000 per year), excluding migration.
How big is a megacity, and where are most of them? 10 million or more people. Most are in lower- and middle-income countries, mainly Asia and Africa — China and India are forecast to hold the most.
What is the difference between a refugee and an IDP? A refugee has crossed an international border; an IDP is forced to flee but stays inside their own country.
Name one social consequence for a source area and one for a destination. Source: an ageing, shrinking community as young adults leave. Destination: a younger but overcrowded population straining housing and services.
Why is voluntary internal migration 'voluntary' and 'internal'? Voluntary = the person chooses to move (not forced); internal = they stay inside the same country, crossing no border.
🎯 Highest-yield exam reminders
Exam Tips
- For a pyramid, line graph or map: DESCRIBE first (shape, highest/lowest, a figure WITH UNITS, any clustering), and only Explain if the command asks — Describe needs no reasons.
- Learn the figures exactly: megacity = 10 million+; replacement is not needed here, but natural increase = births − deaths (no migration).
- Keep the scales straight — individual vs wider society for megacities; source vs destination for migration. Examiners reward answers that name the scale.
- Refugee = crossed a border; IDP = stayed inside the country. Forced = no choice (pushed); voluntary = a chosen move (pulled).
- Always name real cases: Syria, Lake Chad and Three Gorges Dam for forced migration; Queensland/NSW for internal migration; Delhi or Lagos for megacities.
- On the [10] Examine/Evaluate, weigh both sides with named places and figures, then finish with an explicit, justified judgement.