Imagine a city so large that its population could fill Wales twice over. A megacity holds more than 10 million people — a tide of humanity that arrives faster than roads, pipes and homes can be built. In 1950 there were just two; today there are more than thirty, and most of the newest ones are in poorer parts of the world.
Why megacities grow so fast
Rapid growth in a lower-income country (LIC) or newly emerging economy (NEE) has two engines. First, rural–urban migration: people move from the countryside chasing jobs and services (pull) or escaping hardship on the land (push). Second, natural increase: migrants are often young adults who then have children in the city. Because both engines run at once, some megacities have added a million people in a single year — far faster than any city could build homes, lay pipes or hire teachers.
Opportunities and challenges
| Opportunities | Challenges |
|---|---|
| More jobs and higher wages | Squatter settlements (informal housing) |
| Schools, clinics, universities | Traffic jams and air pollution |
| Electricity, phones, internet | Shortages of clean water and sanitation |
| Culture, trade and ideas | Waste disposal and poor drainage |
When homes cannot be built fast enough, new arrivals may construct their own on unused land — forming squatter settlements (sometimes called slums or informal settlements). These are not lawless dumps; they are often busy, resourceful communities. But without proper water, toilets and secure ownership, disease spreads and families cannot invest in their homes.
Towards a sustainable city
A sustainable city meets today's needs without wrecking the future. Practical steps include upgrading (not bulldozing) informal settlements by adding water pipes and toilets, running clean and cheap public transport, recycling waste and water, planting green spaces, and using solar power. Small, affordable improvements often work best because residents can maintain them.