1. A computer implemented method performed by a mobile device, comprising: receiving a request for configuring a geographic region, the geographic region being associated with an application program, the application program to be invoked when the mobile device enters the geographic region; responsive to the request, configuring the geographic region through an application programming interface, the configuring including specifying one or more first call parameters according to a first calling convention defined by the application programming interface, where at least one first call parameter specifies a center of the geographic region; monitoring a current location of the mobile device; determining that the mobile device has entered the geographic region based on the monitoring; and invoking the application program upon the determining.