The trend toward ever greater urbanization continues unabated across the globe. According to the United Nations, by 2025 closes to 5 billion people will live in urban areas. Many cities, especially in the developing world, are set to explode in size. Over the next decade and a half, Lagos is...

The trend toward ever greater urbanization continues unabated across the globe. According to the United Nations, by 2025 closes to 5 billion people will live in urban areas. Many cities, especially in the developing world, are set to explode in size. Over the next decade and a half, Lagos is...

This paper proposes a simple theory of a system of cities that decomposes the determinants of the city size distribution into three main components: efficiency, amenities, and frictions. Higher efficiency and better amenities lead to larger cities, but also to greater frictions through...