Knowledge Organiser: Megacities and Rapid Urban Growth
Key Terms
- Megacity: City with 10m+ population
- Rural-urban migration: People moving from countryside to city
- Push factor: Drives people FROM rural areas
- Pull factor: Attracts people TO cities
- Informal settlement: Housing built without legal permission
- Top-down development: Led by governments / large organisations
- Bottom-up development: Community-led approaches
- NEE: Newly Emerging Economy (e.g. India, Brazil)
Key Data
- 1950: 2 megacities → 2024: 37 megacities
- 90% of megacity growth in LICs/NEEs (Africa/Asia)
- Dhaka: 22.5m people, +300,000/year
- Mumbai: 21.4m people, 6.6% of India's GDP
- Dharavi: 1m people, 2.4km², £1bn economy
- 1 billion people globally in informal settlements
- Mumbai traffic: 10 km/h; Dhaka traffic: 7 km/h
- Urban wages: 3–5× higher than rural wages
Case Studies
- Mumbai (NEE): Dharavi slum with £1bn economy; flooding 2005 (944mm/day); Mumbai Metro Line 3 (33.5km); Slum Rehabilitation Authority
- Dhaka (LIC): 40% in bastis; Rana Plaza 2013 (1,134 dead); BRAC reaches 100m people; ADB flood embankments
- Rio de Janeiro: Favela-Bairro — community upgrades not demolition
- Seoul: Demolished urban highway → restored Cheonggyecheon stream
- Singapore: Certificate of Entitlement system limits car ownership
Must-Know Facts for Exams
- Name your city in sentence 1 of any case study answer
- Use TRAFFIC acronym for megacity challenges
- Top-down: better for infrastructure at scale
- Bottom-up: better for reaching marginalised communities
- Best approaches combine both (e.g. Favela-Bairro)
- Informal settlements are NOT just poverty — Dharavi has a £1bn economy
- Dhaka = LIC | Mumbai = NEE | Tokyo = HIC (know the difference)
- Climate change is worsening megacity flooding — link topics for synoptic marks
Common Mistakes
- Writing about informal settlements as purely negative: Dharavi (Mumbai) has a £1bn informal economy with 15,000 single-room factories — always show the economic activity alongside the health and infrastructure challenges
- Confusing top-down and bottom-up approaches: Top-down (e.g. Mumbai Metro Line 3) delivers large infrastructure but can displace communities; bottom-up (e.g. BRAC in Dhaka) reaches the poorest but is limited in scale — evaluation answers must compare both
- Using only one megacity example: AQA questions often ask you to compare cities at different development stages — use Dhaka (LIC), Mumbai (NEE) and Tokyo (HIC) to show the full spectrum
- Not linking urbanisation to development level: 90% of current megacity growth is in LICs/NEEs (Africa and Asia) because HICs urbanised earlier — always explain WHY growth is concentrated there, not just WHERE
Memory Aid
- T — Traffic congestion (Mumbai: 10 km/h; Dhaka: 7 km/h — costs Bangladesh 3% of GDP annually)
- R — Resources under strain (water, electricity, food systems overwhelmed by rapid growth)
- A — Air pollution (Mumbai PM2.5 levels 5× WHO limit; 7 million deaths/year globally from urban air pollution)
- F — Flooding and environmental risk (Dhaka: 70% below 6m sea level; Mumbai 2005: 944mm in 24 hours)
- F — Finances and informal economy (60% of LIC urban workers in informal economy without legal protections)
- I — Informal settlements / Infrastructure gap (1 billion people in informal settlements globally; infrastructure always lags population)
- C — Congestion of services (schools, hospitals, waste collection overwhelmed — Dhaka generates 35,000 tonnes waste/day)
- Mumbai numbers to know: 21.4m population | 6.6% of India's GDP | Dharavi: 1m people in 2.4km² | £1bn Dharavi economy | 15,000 factories | 10 km/h traffic | 944mm rain July 2005 | Metro Line 3: 33.5km
- Dhaka numbers to know: 22.5m population | 300,000 new arrivals/year | 40% in bastis | 7 km/h traffic | 35,000 tonnes waste/day | Rana Plaza 2013: 1,134 dead | BRAC: 100m people reached
- Global facts: 37 megacities in 2024 | 90% of growth in LICs/NEEs | 1 billion in informal settlements | 2050: Africa's urban population triples