This Is Africa's New Biggest City: Lagos, Nigeria, Population 21 Million

The West African metropolis has surpassed Cairo in size, according to the New York Times.

In a celebration of Lagos and African urbanization, the Financial Times ran a piece by Xan Rice highlighting Nigeria's commercial capital's size, its economic importance, and its government's energy in addressing concrete urban problems.
The UN estimated the city's population at 11.2 million in 2011. The New York Times estimates that it is now at least twenty-one million, surpassing Cairo as Africa's largest city. It is clear that whatever the size, and however the city is defined, Lagos is the center of one of the largest urban areas in the world. With a population of perhaps 1.4 million as recently as 1970, its growth has been stupendous. Rice estimates that Lagos generates about a quarter of Nigeria's total gross domestic product. The center of Nigeria's modern economy, Lagos has many millionaires, but Rice estimates that two thirds of the population are slum dwellers.
Lagos is fortunate in that one energetic governor, Babatunde Fashola, succeeded another, Bola Tinubu. Tax revenue now exceeds $92m per month, up from $3.7m per month in 1999. Fashola says that tax rates have not increased--but clearly enforcement has. Tax collection, in a system that recalls tax farming in the New Testament or under Louis XIV, is apparently performed by a private company with links to Tinubu. The company retains 10 percent of all revenue collected over a certain threshold (at present, $43m per month). With the revenue, Fashola has launched genuinely impressive transportation and sanitation initiatives that range from construction of a city rail network, bus lanes, and filling potholes to more efficient trash collection.
The energy and other initiatives implemented by the city government are in stark contrast to the poor governance and paralysis that characterizes most of the rest of Nigeria. Meanwhile, the city continues to grow explosively. If jobs in the modern economy are to be found, it will require substantial new investment in education. Nationwide, there has been remarkably little for a generation, with the exception of the rapid expansion of the university system--itself underfunded. But, Lagos illustrates what is possible when the government enters into a social contract with its citizens whereby in return for taxes, it provides services. 

in The Atlantic.