Big cities feed on hinterlands to sustain growth: Study

Large cities depend on their hinterlands to sustain growth, thereby increasing the urban-rural divide in economic prosperity and individual life chances, according to a study.

Individuals who leave small areas for large cities are better educated and have higher cognitive abilities than those who stay, said researchers from the Linkoping University in Sweden.

The findings, published in the journal Science Advances, provide 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," said Marc Keuschnigg from Linkoping University.

Selective migration of highly productive individuals to cities explains a substantial part of urban growth, according to the researchers.

The research has established that population size is the single most important factor in the functioning of cities.

Many social and economic indicators increase not simply proportionally to city size but are subject to nonlinear dynamics.

Doubling city size, for example, reportedly raises total income, the number of patents, the number of residential moves, and the number of romantic breakups by roughly 115 per cent.

This suggests urbanites' productivity and pace of life increase as their cities grow.

The extra 15 per cent is referred to as "superlinear scaling" or the +15 per cent phenomenon.

The mathematical models proposed to account for these regularities suggest that superlinear scaling of urban outputs is a consequence of increased social interaction in dense urban environments.

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.

Urban scaling researchers see the +15 per cent phenomenon as a self-reinforcing process that produces winners but no losers, implying that urban growth is socially beneficial to contemporary societies in general.

Utilising Swedish register data with unique granularity, the study tests whether the +15 per cent phenomenon truly can be attributed to increased social interconnectivity in cities.

Their geocoded micro-data capture the dissimilarities in the population composition between metropolitan areas of different size and provide better information on the micro-mechanisms responsible for observed non-linearities.

The research found that social interactions explain only half of the previously reported agglomeration effects and, in contrast to existing explanations of super-linear urban scaling, they find that differences in population characteristics between metropolitan areas crucially 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," said Keuschnigg.

Those moving from smaller areas to one of the Sweden's larger cities have, on average, 1.8 more years of education and their cognitive ability is 0.4 standard deviations higher than for those who stayed, researchers said.

This is consequential for societies because strongly selective migration has cumulative effects on local populations in both sending and receiving regions, they said.