First identified by Stanley Milgram in the 1972 paper The Familiar Stranger: An Aspect of Urban Anonymity,[1] it has become an increasingly popular topic in research about social networks and technologically mediated communication.
But if such individuals meet in a different setting, for example a different city or off the street, they are more likely to introduce themselves than would be perfect strangers, as they have a background of shared experiences.
Early experiments on familiar strangers by Milgram involved researchers visiting train stations and university campuses to survey people about who they recognized.
With the advent of widespread social media and urban analytics, researchers have used new datasets to understand familiar strangers, including public-transportation usage[3] and web blog networks.
Finally, he noted that breaks in routines, such as health emergencies or natural disasters would cause familiar strangers to interact with each other.
The 1972 paper was based on two independent research projects conducted in 1971, one at City University of New York and the other at a train station.
They too found evidence of "socio-metric stars" who stood out to many people due to unique visual characteristics like a wheelchair, flowers, or dirty long hair.
There have been a number of studies that have further characterized the relationship between familiar strangers using automatically generated sets of data from urban systems.
Using bus usage data, it was found that a person's set of familiar strangers is highly based on routine and daily behavior.
Wi-Fi usage data for university campuses have provided additional datasets for analyzing familiar strangers.