Researchers at Linköping University in Sweden have quashed a common theory of the self-reinforcing dynamics of urban growth and have shown that big cities feed on their hinterlands to sustain growth, thereby escalating the urban-rural divide in economic prosperity.

The research found that individuals who leave small areas for large cities are better educated and have higher cognitive abilities than those who stay, and provides a more nuanced account for the reasons behind the increasingly uneven economic geography observed in many countries, with growing levels of inequality between urban and rural areas.

"Our research shows that people who leave rural areas for cities are, on average, better educated and have higher cognitive abilities. This selective migration fuels the higher than expected outputs of big cities and, at the same time, adds to the cumulative decline of less populated regions," says Dr. Marc Keuschnigg, the lead author from Linköping University's Institute for Analytical Sociology.

Thus, selective migration of highly productive individuals to cities explains a substantial part of urban growth, according to the Linköping researchers' study.

The research has established that population size is the single most important factor in the functioning of cities, so therefore, doubling city size, for example, raises total income, the number of patents, the number of residential moves, and the number of romantic breakups by roughly 115 percent—suggesting that urbanites' productivity and pace of life increase as their cities grow. The extra 15 percent is often referred to as "superlinear scaling" or the +15 percent phenomenon.

In large cities, there are more people to exchange ideas with, as well as to cooperate with in bringing about innovations, new forms of social life, and additional wealth. Consequently, due to urban scaling, providing the +15 percent phenomenon as a self-reinforcing process that produces winners but no losers, implying that urban growth is socially beneficial to contemporary societies in general.

The research also found that social interactions explain only half of the previously reported agglomeration effects and, in contrast to existing explanations of superlinear urban scaling, differences in population characteristics between metropolitan areas drive the phenomenon.

"Our results are of considerable policy relevance, because they identify the migration of talented people from smaller areas to larger cities as an important force behind observed agglomeration effects" says Dr. Marc Keuschnigg.

Credit: and Linköping University.