How Facebook recommends this random person you only met once

I wrote before about designing for creepiness, which is this simple idea that companies should inform users about why something is recommended to avoid freaking them out on how the service got to this info.

Recently in multiple conversations with people, it came to my attention that many are surprised by how Facebook recommended this person whom they only met once with nothing common.

For those who don’t know how it works, it is very simple. Facebook matches information from multiple sources to identify a person to recommend, then the software ranks those people based on a specific criteria that’s only known  to those inside Facebook, and decides which accounts to display.

So, here is a list of possible ways by which Facebook recommends friends (I don’t know which ones they actually use):

  • If you give Facebook access to your email contacts, it will match those emails with Facebook accounts and starts recommending users using Facebook with the same email in your contacts list.
  • If someone has just joined the network and started to get a lot of friends who are mutual with you, Facebook will assume you also know this person and will recommend him/her for you.
  • If someone is using the same computer to login to Facebook, Facebook might recommend friends of that user to you on the basis they might be mutual. (If you use multiple accounts on the same computer you will notice this).
  • Facebook owns WhatsApp, for WhatsApp to work it needs access to your phone contacts, and it uploads them to the servers. If Facebook knows that I have your phone number on my phone it can start recommending you to me and visa-versa.
  • If you and I meet in the same location everyday from 9-5 (Facebook knows that from our phone location, or the network we use to login to our accounts like work network). If one of us lists on their account where they work (Or even without that), it will consider us working at the same place and start recommending us to each other along with other work mates.
  • If we both attended the same event (Visited the event page, said attending or maybe..etc) then our GPS locations confirmed our location at the time of the event, it might start recommending us to each other.
  • If we are in a group picture with mutual friends, it will definitely recommend us to each other.
  • This one is interesting: If you stalk someone by visiting their profile, Facebook can start recommending you to this person.
  • If two friends have your number/email, one of them is your friend, Facebook will recommend the other one as your friend.

This is what I got on top of my mind, what other ways Facebook might be matching information to recommend you friends?