How Nigeria surpassed South Africa as Africa's largest economy.

Nigeria's overnight transformation raises two distinct but interconnected questions. First: What do we miss about countries when we don't have accurate economic data about them—and what are the practical implications of that blindness? In computing its GDP all these years, Nigeria, incredibly, wasn't factoring in booming sectors like film and telecommunications. The Nigerian movie industry, Nollywood, generates nearly $600 million a year and employs more than a million people, making it the country's second-largest employer after agriculture.

As for the telecom industry, consider that there are now some 120 million mobile-phone subscribers in Nigeria, out of a population of 170 million. Nigeria and South Africa are the largest mobile markets in sub-Saharan Africa, and cell-phone use has been exploding in the country. Incorporating the film and telecom industries into Nigeria's GDP made a huge difference in the services sector, rendering the country's economy not just bigger but more diversified.