Growth in population and area: globally and at city level

Imagine a city as a plant that starts as a tiny seed (a small settlement) and, over time, spreads its roots (population) and shoots out branches (area). This analogy helps us understand how cities grow both in the number of people and the land they occupy.

Key Facts

• In 2020, 54.2 % of the world’s population lived in urban areas.
• By 2050, this is projected to rise to 68 % (UN, 2018).
• Fastest urbanisation occurs in Asia and Africa – cities like Nairobi, Lagos, and Jakarta are expanding rapidly.

Population Growth Formula

$P_t = P_0 \times (1 + r)^t$ where $P_0$ = initial population, $r$ = annual growth rate, $t$ = years.

Example: If a city has 1 million people and grows at 3 % per year, after 10 years it will have: $P_{10} = 1{,}000{,}000 \times (1 + 0.03)^{10} \approx 1{,}343{,}916$ people.

Area Expansion

Urban area often grows faster than population because of sprawl and new housing developments.

1. New suburbs are built on former farmland.
2. High‑density housing (apartments) increases population without expanding area.
3. Infrastructure projects (roads, rail) can push city limits outward.

1. Lagos, Nigeria

Population ≈ 14 million (2020). Growth rate ≈ 3.5 %/year. Area expanded from 1,171 km² to 3,000 km² in the last two decades due to rapid suburbanisation.

2. Singapore

Population ≈ 5.7 million (2020). Growth rate ≈ 1.0 %/year. Area is fixed (≈ 720 km²) – growth is achieved through vertical development (skyscrapers) rather than horizontal expansion.

Remember the Key Questions

1. What are the main drivers of urban growth? (e.g., migration, natural increase, economic opportunities)
2. How does population growth differ from area growth? Provide examples.
3. Explain the concept of urban sprawl and its environmental impacts.
4. Use data to support arguments – show tables or graphs where possible.

Practice Question

A city has a current population of 2 million and an annual growth rate of 2 %. Calculate its population after 15 years. Show your calculation using the formula above.

Answer: $P_{15} = 2{,}000{,}000 \times (1 + 0.02)^{15} \approx 2{,}000{,}000 \times 1.3499 \approx 2{,}699{,}800$ people.