The African city with the largest population is Lagos, Nigeria. In 2014, the city was estimated to have a population of 21 million people.
The population in Lagos jumped significantly in a short period of time. In 2011, it was estimated to only have 11.2 million people. Prior to then, Cairo was the most populous city in Africa. Lagos is thought to be responsible for one-fourth of Nigeria's gross domestic product.
An oil boom and a growing economy are thought to contribute to the fast population growth. The country also has a high birth rate that helps boost its numbers.