More than half of the world’s population currently lives in cities – and as time goes on, it’s clear that more urban dwellers will find themselves living in megacities. Megacities are defined as urban areas with a population of more than 10 million people. Today, more than 80% of people in higher income countries find themselves living in urban areas, and in upper-middle income countries the number lies between 50-80%. Rural-to-urban migration is an increasingly relevant trend in the 21st century. Prospects of better job opportunities and higher wages, along with shifts from agrarian to industrial and service-based economies, are causing mass movement to cities.
While there are certainly downsides to mass urbanization, like pollution and overcrowding, the upsides clearly outweigh the negatives for most people. Convenience, better jobs, easier access to social services, and higher wages are among the many reasons people are likely to continue to move to cities. With the emergence of smart and green cities, the quality of life for many urban dwellers will likely continue to improve, and more large urban areas will morph into megacities.
Here are the top 20 most populous cities in the world.
| Rank | City | Population |
| 1. | Tokyo, Japan | 37,274,000 |
| 2. | Delhi, India | 32,065,760 |
| 3. | Shanghai, China | 28,516,904 |
| 4. | Dhaka, Bangladesh | 22,478,116 |
| 5. | São Paulo, Brazil | 22,429,800 |
| 6. | Mexico City, Mexico | 22,085,140 |
| 7. | Cairo, Egypt | 21,750,020 |
| 8. | Beijing, China | 21,333,332 |
| 9. | Mumbai, India | 20,961,472 |
| 10. | Osaka, Japan | 19,059,856 |
| 11. | Karachi, Pakistan | 16,459,472 |
| 12. | Chongqing, China | 16,382,376 |
| 13. | Istanbul, Turkey | 15,415,197 |
| 14. | Buenos Aires, Argentina | 15,257,673 |
| 15. | Kolkata, India | 14,974,073 |
| 16. | Kinshasa, Democratic Republic of the Congo | 14,970,460 |
| 17. | Lagos, Nigeria | 14,862,111 |
| 18. | Manila, Philippines | 14,158,573 |
| 19. | Tianjin, China | 13,794,450 |
| 20. | Guangzhou, China | 13,635,397 |
