Positioning at Decimeter accuracy for GIS Applications Using GPS Handheld Receivers Dr. Ahmed El-Mowafy Associate Professor Associate Professor, United Arab Emirates University, UAE Email: Ahmed.mowafy@uaeu.ac.ae This study presents a system developed for base map generation and point position determination in GIS at the decimeter level accuracy using commercial Garmin handheld GPS receivers. The system downloads carrier-phase and code measurements of GPS handheld receivers online to a palmtop or laptop, and simultaneously registers the point code and description. To achieve decimeter positioning accuracy, the data is post processed in a differential mode with measurements from a reference station. Main characteristics of the proposed system are discussed, with focus on tracking of low elevation satellites, lock performance to satellites while in motion, phase measurement noise experienced, and the impact of receiver dynamics on system performance. The required occupation time per point is also investigated. Some guidelines for system operation are proposed. To evaluate the performance of the proposed system, several tests in the static and kinematic modes were carried out. Test results showed that for a 95% probability, the positioning accuracy of the proposed system is generally less than 15 cm (2 sigma). With such achievable accuracy and a cost that is a fraction of that of the currently used geodetic-grade GPS receivers, the system represents a cheap alternative for a wide range of precise GIS applications.