The world is becoming increasingly urban as the world's population grows. Out of Earth's population of more than seven billion, over half live in urban areas – in cities, suburbs and towns. A significant proportion of the global population – nearly one quarter – live in cities of more than a million or more. More and more people are also living in so-called "megacities", which have populations of more than 10m or more.

Research by UK government statisticians shows London will likely reach "megacity" status by 2039, as the population grows from the current 8.5m to 11m. On World Cities Day, we look at some of the biggest cities in the world, as defined by their population according to data from Demographia World Urban Areas.

Tokyo-Yamahama

Tokyo
Tokyo-Yokohama has a population of 37,843,000 and a land area of 3,300 square milesReuters

Jakarta

Jakarta
Jakarta has a population of around 30,539,000 and a land area of 1,245 square milesReuters

Delhi

Delhi
Delhi has a population of 24,998,000 and a land area of around 800 square milesReuters

Manila

Manila
Manila has a population of around 24,123,000 and a land area of around 610 square milesReuters

Seoul

Seoul
Seoul-Incheon has a population of around 23,480,000 and a land area of around 875 square milesReuters

Shanghai (SHG-JS-ZT)

Shanghai
Shanghai (SHG-JS-ZJ) has a population of around 23,416,000 and a land area of 1,475 square milesPaul Reiffer/www.paulreiffer.com

Karachi

Karachi
Karachi has a population of around 22,123,000 and a land area of around 365 square milesReuters

Beijing

Beijing
Beijing has a population of around 21,009,000 and a land area of around 1,475 square milesReuters

New York NY-NJ-CT

New York skyline
New York (NY-NJ-CT) has a population of around 20,630,000 and a land area of around 4,495 square milesGetty

Guangzhou-Foshan

Guangzhou
Guangzhou-Foshan has a population of around 20,597,000 and a land area of around 1,325 square milesReuters