City size plays crucial role in migration patterns

The study, published today in the open access journal PLOS ONE, looked at internal migration patterns across the USA, finding that the size of origin and destination cities play a crucial role in the behaviour of people who move from one place to another.

Inhabitants of smaller cities -- of fewer than 100,000 inhabitants -- are twice as likely to migrate than those of cities with a population greater than ten million. Those who do migrate are more likely to move to a city of a similar size.

People already living in larger cities are less likely to migrate, but when they do, they are more likely to move to similarly sized large cities.

Lead researcher, UCL PhD student Rafael Prieto Curiel (UCL Mathematics), said: "The results could have an impact on future integration policies as governments can more accurately predict where citizens are likely to move from and to within their country.

"Migrants contribute to the prosperity of their destination with skills and activities, but migration requires integration policies and social support systems to allow newcomers to settle into a new environment and therefore fully contribute locally."

Ensuring newcomers are able to settle into a new area and contribute their skills and expertise can be important in combatting issues such as segregation, inequality and loneliness.

Professor Steven Bishop (UCL Mathematics) said: "The new scaling model has not previously been used to identify migration patterns. It applies a mathematical formula to migratory patterns relative to city size. When taken into account along with other existing models that focus on the distance between origin and destination cities, we have found that the laws of scaling are a significant feature of human migration patterns.

"The model can be used to more accurately predict population movement as it corrects biases which occur in other methods. This is an important, data-led development in revealing how communities and regions will grow and develop in the future."

The study considered a city as having more than 50,000 inhabitants, with anywhere less than this considered to be a rural area. The cities considered varied from populations of just over 50,000 to nearly 20 million in the New York metropolitan area.

The researchers found that international migration follows a different pattern, with individuals more likely to head to a large city where they are perhaps more likely to find jobs, housing and other people of a similar culture. More data on the origins of international migrants is needed to extend this work.

The research followed a collaboration between UCL, Italy's national research body Consiglio Nazionale Delle Ricerche (CNR) and the University of Pisa.

The project was supported by the Mexican Government via a Conacyt Scholarship, the EU project SoBigData and the Cimplex project funded by the European Commission.