Strategies for Merging GPS and Terrestrial Geodetic Network Iraj Jazireeyan Lecturer K.N.Toosi University of Technology, Iran Email: jazirian@kntu.ac.ir, jaziryan@yahoo.com Iraj Jazireeyan Lecturer K.N.Toosi University of Technology Email: jazirian@kntu.ac.ir Abstract Horizontal terrestrial geodetic control networks are the most important and valuable in each country, because for establishing them time and expenses have been paid. Today the advent of the Global Positioning System, survey points could, both technically and economically be accessible to user for network densification, but the use of the terrestrial network and merge them with the new network is required. In order that the integrity of the control networks may be maintained or improved when we add the new observations or new GPS network, we minimize the requirements for altering published coordinate values and the methods for merging these networks and their statistical analyses must be chosen carefully. Several approaches are reviewed in this study and discuss some of the problems that must be overcome, but the main weight is given to the weighted constraint approach. The basic methods are examined here emphasis on the statistical analysis of resulting control coordinates differences for terrestrial and GPS network then the problems that caused distortions in each of the networks are reckoned. A numerical example is given for the practical use of the merging methods and conclusions are drawn concerning the approach which should be adopted for networks combination.