One example embodiment relates to a method that comprises receiving, via a first portable electronic device, contextual information and a geolocation relating to a first user in a network-based system; receiving, via second portable electronic device, contextual information and a geolocation relating to a second user in the network-based system; identifying a common element in the received contextual information relating to the first user, and the received contextual information relating to the second user; in response to an identification of the common element, defining a boundary for a geofence based on the geolocation of the first or second users, and redefining the boundary of the geofence to exclude at least one member from the population, the exclusion based on an identified change in geolocation or contextual information relating to the at least one excluded member.