Positional accuracy of GPS measurement has been based on simulation and actual measurement due to the difficulty of conducting 24-hour actual running tests. However, the conventional measurement is only based on brief evaluation; hence variability of positional accuracy which varies depending on measurement time and location had been an issue. Thus, it is significant to show the validity by the estimation of positional accuracy, and actual measurement using of lengthy simulation.In this study, actual measurement data in an urban area was obtained for long hours, and a simulation using 3D maps was implemented. A high precision positional measurement system was equipped on a vehicle in order to collect actual measurements and positional data at each measurement time. The data obtained by the measurement system was used as the reference coordinate for both the simulation and the actual measurements. Consequently, comparison between the simulation and actual measurement data on positional accuracy was able to be implemented for the first time. A dominant deterioration factor of positional accuracy is multipath error caused by reflection from the likes of buildings. Thus, reception status of incoming waves from GPS at each measurement time and reception point by simulation. Specifically, if a satellite which receives direct waves was exclusively used in simulation, measurement accuracy shall be improved. Thus, improvement of the accuracy was verified by choosing the same satellite used in simulation. Consequently, significant improvement in the measurement accuracy was affirmed, and the validity of satellite measurement simulation using 3D maps was partially verified.