Global cities, sometimes referred to as world cities, are often the most important cities in the world in terms of economic and cultural impacts. These cities, such as London, New York and Paris, are not always the largest cities, but they play an important role in economic links with other countries.

The world's population is growing rapidly, and as of June 2017 stood at 7.4 billion people. The highest rates of population growth are occurring in low income countries (LICs), such as Zimbabwe, Malawi and Niger. Some countries are experiencing population decline, for example Japan, Russia and Ukraine.

Today more than 50 per cent of the world's population live in urban areas. The number of cities with over 10 million people is increasing. These are called mega-cities.

In 2017 there were 34 mega-cities in the world. The table shows the top ten mega-cities in 2015.

Eight out of ten mega-cities are located in Asia.