It has traditionally been measured in terms of how close the parental residences of bride and groom are to each other. I think a new measurement is needed today. If we go back to the 1930s we can see clear propinquity patterns, measured the traditional way. For your parents propinquity still mattered - most, I bet, married some who grew up in the same town or city. For you, because the age of marriage has increased and because most of you will marry well after graduating from college, it is unlikely that you will marry someone who grew up within 20 blocks of your parents' home.
Propinquity still operates, but it operates in a different context.
Where you will be living and working after graduating from college will be influential in terms of your mate selection process. Now interaction networks have changed - who your neighbors are and who your fellow workers are, this is the group of importance now. We live in a society with much segregation in residence patterns. There are white, middle class suburbs, and black, lower class central city slums. There are college campuses, like this one, where lower class groups and non-Catholics are scantily represented.