Interestingly, personal relationships persist once these moves have occurred, and people tend to trade in a way correlated with that of their cube-mate from three months ago; although, reassuringly, they do not trade in a way correlated with their future cube-mate. (I say “reassuringly” because this is a useful way of testing whether our results reflect Google seating people with similar opinions near each other, rather than people near each other influencing the opinions of others.)
Most information flows tend to travel very short distances; save the relationship you have with someone who used to sit next to you. Migration works in much the same way. Available information often informs where someone will move. Tacit knowledge does not travel well (hence the micro-clustering of innovation), resulting in short distance people flows. But a trusted friend, neighbor or family member who moved all the way across the country can facilitate long distance relocation.
Think of Parochial Pittsburgh as part of an office crowded with cubicles and the value of the relationships that move all the way to the other side of the room (United States) every 3 months.