Detroit and Wayne County’s “social connectedness” show strong ties within the Mitten as well as some peripheral connections to the south, Mississippi, Alabama, and Georgia. The southern ties are most likely related to the Great Migration of African Americans to northern industrial cities.

More from NYTimes:

This map shows an index of connectedness, created using friendship links between pairs of anonymous Facebook users from a snapshot of the platform in April 2016. The researchers aggregated the links at the county level, so neither the Times nor other academics working with the data can identify individual users within it, or how many Facebook users live in each county. Because counties with more people invariably have links to more places, this map rescales the index to account for differences in population.