In the paper the author`s application called OLMAP for determination of an observer position on numerical maps is presented. This application integrates GPS receiver`s position with numerical maps during the measurements in real-time taking advantage of DGPS and RTK techniques. One of the options of this application is positioning or/and monitoring of moving GPS antenna on a numerical map indicating the speed and direction of vehicle movement. Positions of moving GPS antenna may be obtaned with the accuracy of 1-2 meters in DGPS mode or 1-3 centimeters in the RTK mode. The OLMAP application can be also successfully used for Geographic Information Systems (GIS) and Land Information Systems (LIS).