A global positioning system (GPS) geodetic network has been established at the western end of the North Anatolian Fault Zone (NAFZ) in the Marmara Sea Region (Turkey) with a density of 47 points to determine the velocity field. Some attention is paid to the determination and testing procedures. This study focuses on the purpose of determining methods of crustal movements with GPS, deformation analysis, the reliability of conclusions, and the character of the deforming area. Displacements are determined by using the method of S-transformation. The analysis of the deformation field was performed both in two and three dimensions. Testing procedures for deformation measurements are derived. Subsequently rotation and translation of the objects are studied. The results of the proposed test methods are independent of the coordinate system chosen. Two large earthquakes on the region with magnitudes of 7.4 and 7.2 in 1999 show the importance of such studies to submit references to other scientists.