1. A method performed by data processing apparatus, the method comprising: receiving, at a computer system, a plurality of requests from a corresponding plurality of users, each request to form a respective association with the computer system, and wherein each request includes data associated with a respective user of the plurality of users, wherein the computer system is associated with a central entity to which each user of the plurality of users sends each request to form the respective association, wherein the central entity is an event scheduled to occur at a geographic location; creating, at the computer system, a network including the plurality of users in response to receiving the plurality of requests; storing, at the computer system, data associated with each user of the plurality of users; detecting that each user of a subset of users of the network has performed a common operation at the computer system, wherein the common operation includes transmitting a registration request using a mobile device to the computer system associated with the central entity; providing, to at least one user of the subset of users, at least a portion of data associated with at least one other user of the subset in response to the detecting; determining that a first user and a second user have transmitted respective registration requests to the computer system; displaying, on a mobile device associated with the first user, a first distance of the first user and a second distance of the second user from a common geographic location; and terminating the network after an expiration of the event.