Abstract: A computer system is disclosed in which a touch-screen display (10) displays a map to a user. The user can select a location on the map and an indicator (50) is displayed on the map at the selected location. A server processor (18) is provided to modify a first aspect of the appearance of the indicator (50) in dependence on the time that has elapsed since the location on the map was selected. A reinforcement tool is also provided so that a user can endorse an indicator (50), and the server processor (18) can modify an aspect of the appearance of the indicator in dependence on the number of endorsements received. A GPS receiver (12) is also provided so that the user device (2) can generate an alert when the position determined by the positioning device is within a predetermined range of a location of interest.