Geodesy, the science of measuring the Earth's shape and positions on it, allows the measurement of plate motion directly using GPS, the Global Positioning System. This network of satellites is more stable than the Earth's surface, so when a whole continent moves somewhere at a few centimeters per year, GPS can tell.
GPS uses a system of satellites to triangulate the position of a receiver anywhere on Earth. By using a network of receivers near plate boundaries, scientists can very accurately determine how the plates behave
