Fuente: Wipo "precision agriculture" A location system is used in a vehicle moving within an area at a selected speed and in a selected direction. A heading sensor provides a heading signal representing the direction of movement of the vehicle. A speed sensor provides a speed signal based on available reference signals representing the speed of the vehicle. A storage device stores initial position data representing a selected initial position of the vehicle and checkpoint data representing a navigation checkpoint location. A database stores a plurality of records which each include geographic information data representing selective aspects of the area. A processor estimates a current position signal representing an estimated current position of the vehicle based on values of the heading signal, values of the speed signal, the initial position signal, and on previous values of the current position signal. Values of the current position signal correspond to records stored in the data base. A correction device selectively corrects the current position signal based on selected position inputs which indicate an approximate vehicle position relative to the navigation checkpoint location. An alerting device obtains an alerting signal indicating that the vehicle has reached a selected region within the area based on the current position signal and the geographic information data.