Fig 2. Probability of migration conditional on city size.

Probability of migrating from a city of a given size (horizontal axis) to a city of a given size (vertical axis). The fitted values of $\widehat{\beta }$ according to the city size (plotted in the lower panel) indicates if the probability of migrating to a destination with a given size follows a sublinear ($\widehat{\beta }<1$, in blue) or superlinear ($\widehat{\beta }>1$, in orange) behaviour. For example, we observe that if the city of origin is larger than 4 million inhabitants, then the probability of migration follows a superlinear behaviour. In contrast, a strong sublinear behaviour is observed for small cities, particularly if the city has less than 100,000 inhabitants.