A method and system for selecting an external user interface using spatial information is described. In one configuration the floor space of a mailroom is mapped using a two dimensional grid. At least one machine is located on the mapped grid and an associated control zone is defined for that particular machine. The machine includes a wireless transceiver for providing user interface access. An external portable processor with a wireless transceiver is provided with user interface logic for the machine. A user then moves the external portable processor into the control zone of the machine. An indoor positioning system is utilized to provide relative or absolute position information relating to the machine and the external processor. The system determines that the external processor is in the machine control zone and allows the external processor to function as a user interface for the machine.