Examining data from China – the biggest internal migration experience in human history – this column finds that migrants from the same village tend to cluster at the same destination for the same occupation. This pattern is driven by social networks within villages that reduce the moving costs for future migrants, such as the risk of not finding a job.
One of my colleagues, Anja Peleikis, found out the same thing about Lebanese migrants in West Africa. See this article [pdf]. It is also somewhat similar to the case of the Igbo traders that I work with. One finds that the trade in a particular product is dominated by people from the same village, either within or outside the country.