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 satellite availability prediction tools perform satellite visibility predictions without considering terrain or structures that block GPS signals, a major issue in mountainous and urban areas. This paper describes a new Geographic Information Systems (GIS) tool, a customization of ArcGIS named Satellite Viewsheds, which predicts satellite visibility for any place and time while considering line of sight obstructions. Satellite Viewsheds requires a raster surface model, the test date and time, and the orbital properties of the satellites. It produces grids depicting the number of visible satellites and optimal viewing time for every cell in the grid. Satellite Viewsheds allows users to avoid areas of signal loss and choose the best time to map using their GPS receivers. The field test of Satellite Viewsheds proved that the tool performs satellite visibility predictions consistently and accurately. The research outlined in this paper indicates that Satellite Viewsheds is the first tool of its kind.