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.

The darker the color, the greater the relative likelihood that any two people living in two different counties are connected on Facebook. Counties that are broadly tied to more — and more distant — places will color in more of the map. Counties where nearly all ties are very local will look more isolated.

The networks that emerge reveal a distinct social fingerprint for each county, influenced by past migration patterns, geographical features and quirks of the local economy — whether, for example, the county is home to a military base, a resort hub or a booming oil industry.