As elsewhere in the world, population estimates for cities vary greatly according to the criteria used. In particular, it is often difficult to differentiate between a city and a greater metropolitan area. Using the latter definition, the biggest city in the world is Tokyo with about 36m. The loss of countryside between urban areas gives rise to these greater metropolitan areas. They already exist in South Africa's industrial heartland of Gauteng Province, around Johannesburg, and in the Nile Valley around Cairo.
Another greater metropolitan megacity is being created around Kinshasa in Central Africa. As well as being the capital of DRC, satellite towns are now being dragged into the orbit of Kinshasa.
Over the next few years, the most important of these could be Brazzaville, on the other side of the River Congo, in Congo-Brazzaville. Trade and more general interaction between the two capital cities is already increasing on the back of greater stability in both countries, although much obviously remains to be achieved in both.
The governments of the two countries have agreed to build a bridge across the Congo by 2015. With both road and rail links, it would encourage much greater trade, with Kinshasa likely to take on the role of the region's economic capital.
Kinshasa is expected to be the fastest-growing city in Central Africa over the next...