Geodesy
Geodesy, the science of measuring the shape and size of the earth and of determining the exact location of points on the earth's surface. Geodesy also involves the study of the earth's gravity.
An important use of geodesy is in making accurate maps of large areas of the earth; such maps must take into account the curvature of the earth's surface. Geodesy is also used in establishing reference points for navigation systems, in detecting gradual movements between different parts of the earth's crust, and in obtaining information about the earth's interior. Geodesic studies show that the general shape of the earth is not that of a perfect sphere, but rather that of a slightly flattened, pear-shaped spheroid.
In their work, geodesists use such surveying techniques as triangulation and leveling, and surveying systems that can automatically compute the geographical coordinates and elevation of a given point by using radio signals transmitted by artificial satellites. In studying the earth's gravity, geodesists use instruments called gravimeters to measure the relative strength of gravity at different points. Geodesists also analyze changes in the orbits of artificial satellites to calculate variations in the strength of gravity from place to place around the world.