Geodesy: the science of accurately measuring and understanding three fundamental properties of the Earth: its geometric shape, its orientation in space, and its gravity field- as well as the changes of these properties with time. Many organizations use geodesy to map the U.S. shoreline, determine land boundaries, and improve transportation and navigation safety. To measure points on the Earth's surface, geodesists assign coordinates (similar to a unique address) to points all over the Earth. oday, geodesists use space-based tools like the Global Positioning System (GPS) to measure points on the Earth's surface.