When we think of our social networks these days, we usually don't include that girl with the pink mat in yoga class or the man with the blue backpack you see on your morning commute. But according to new research, you and so-called "familiar strangers"—that is, people you see all the time but never talk to—are all part of a real-life hidden social network that could be beneficial to all parties and could also help epidemiologists understand how disease spreads.

The concept of a "familiar stranger" isn't new. The term was first coined in the 1970s to describe people whom you see on a regular basis but never talk to or know anything about. Chances are that if you go to work at the same time every day and ride the same bus every day, you'll begin to notice that people will look similar. The same logic applies to people who, like yourself, hit the gym in the evening, people who shop at the same grocery store and whom you always see in the frozen aisle. You know each other — even if you don't really know each other.

But as Scientific American's Sarah Fecht notes, these informal networks have never really been studied despite scientists' belief that they are important to the way contemporary society works. Enter Lijun Sun and the team at the Future Cities Laboratory in Singapore, with the first study to map out these "familiar strangers" in a metropolitan area. The study looked at 30 million bus trips taken by 2.9 million people. Thanks to smart-card technology, the researchers were able to pinpoint who is riding where, when, and with whom.

What they were looking for were two people on the same bus at the same time, which they called "in-vehicle encounters." They found 18 million of these pairings, repeated roughly once every 24 hours, further discovering that 85 percent of the encounters occurred in the morning. That means that all those random people on the bus with you aren't that random, and that people were a part of solidified social webs they might not have been fully aware of. It also means that people who have routines and are creatures of habit potentially open themselves up to more social opportunities.

"In the end, every Singaporian on the bus is linked to every other Singaporian on the bus," Kay Axhausen, a transport planner with the Federal Institute of Technology in Zurich and one of the authors on the study, told Fecht. "Clearly they can’t know all each other personally, but when you construct the networks for each person, all over these networks link up," Axhausen added. 

That's all good news if you, say, want to ask your morning commute crush out on a date. Show up often enough, and you'll eventually become recognizable. There are some scientific benefits as well, according to Scientific American's Fecht:

The results could have implications for predicting the spread of disease through urban areas. “[T]he microorganisms that can spread from person to person and cause disease don't care whether we, their hosts, know each other or not,” Marcel Salathé, a biologist at Penn State University who was not involved in the new study, wrote in an email toScientific American. Although we tend to think of diseases as spreading through friendship and family ties, he says, it’s important to consider all the routes of transmission, including through networks of strangers. “If you know the structure of these networks, you can much better understand and predict how an epidemic is going to unfold, and who should be given priority with respect to intervention strategies.”

All of this science leads to one conclusion: we should be thankful for our "familiar strangers." That is, unless they're inherently creepy or harboring a virulent new disease.