A "Megacity" refers to a city with a population over 10 million people. Picture if almost twice the population of New York City crammed into one city!

Megacities grow due to economic growth, rural-urban migration, and high natural increase rates. Imagine this like magnets attracting people: the "economic growth" magnet promises better job opportunities, the "rural-urban migration" magnet is driven by the desire for a 'city life', and the "high natural increase" magnet is due to high birth rates, particularly from young adults in the city.

Megacities often have an age structure dominated by young adults. Younger population = higher birth rates, and voila, more growth! Imagine a school where the majority of students are freshmen; it's similar with megacities, but with young adults and babies.

As megacities grow, they tend to "swallow" rural areas and nearby towns and cities, becoming multi-nuclei centres. It's like a giant city octopus, reaching out its arms and grabbing up everything in sight.

Tokyo was the first megacity. It now has a population of about 35 million. That's larger than all of Canada! Mumbai has more people than Sweden and Norway combined.