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The Global Positioning System (GPS) has recently become the significant mapping tool for millions of customers worldwide, providing its users with accurate terrestrial positions almost instantaneously. The functionality of a GPS receiver depends on the number of satellites to which it can establish an unobstructed line of sight. Current tools perform satellite visibility predictions without considering terrain or structures that block GPS signals, a major issue in mountainous and urban areas. This paper will describe a new tool for ArcGIS that predicts satellite visibility considering line of sight obstructions. The tool requires a raster surface model, the test date and time, and the orbital properties of the GPS satellites. It produces grids depicting the number of visible satellites and optimal viewing time in each cell. The new tool allows users to avoid areas of signal loss and choose the best time to map using their GPS receiver.