The Graph Free description

Facebook Graph search makes it easy to do a search by city, because one powerful search parameter for people on the social network involves geography.

You can find Facebook friends by city using either the city where they currently live or their hometown. Both are examples of structured data Facebook stores about users, making it easy to search.

You can also do a Facebook search by city for people you don't know, and based on the privacy settings of each individual, see a list of people living in particular cities who use Facebook that you are not friends with.