Chart: By 2030, Delhi’s Population Will Approach Tokyo’s

According to the UN's World Urbanization Prospects, by 2030, the world is projected to have 41 mega-cities with more than 10 million inhabitants each . Tokyo is expected to remain the world’s largest city in 2030, followed closely by Delhi. The fastest-growing cities will be in Asia and Africa.

But what exactly is a city?

Chandan Deuskar's blog explores exactly this question. There's currently no standard definition of an "urban area" or "urban population" - each country relies on its own definition and collects data accodringly. This is an important area of data to improve - the Sustainable Development Goals include many indicators and targets explicity concerning cities and new standards and approaches such as using satellite imagery may provide more accurate data and definitions.