When large numbers of people live and work together in cities, they generate positive effects that small towns or the countryside can’t replicate. The sheer size of cities enables businesses to mass-produce goods and services at low cost. This makes dense urban areas more productive, which attracts more workers and residents, and so on in a virtuous cycle.

Poor people from the countryside move to cities, where opportunities are much greater and they can move up the economic ladder. Their success inspires other rural residents to enter into urban life and improve their own fortunes. Poverty in lively, thriving cities is a dynamic function, with poor neighborhoods acting as economic incubators for new generations of urbanites. Without cities, humanity would remain mired in poverty. With them, the poor can begin to move up and out of squalor.

The most vital factor in the productivity of cities is the rapid spread of new ideas within crowded urban centers. In-person contacts are many and varied, which stimulates creative thinking. Work groups interact intensively, day after day, their members becoming much more invested in the work than by working alone and communicating from home. People in various careers meet up at conferences, restaurants, bars, and entertainment centers, where their various perspectives and ideas nourish each other’s thinking.