To some extent, geodesy is the study of the shape of the Earth. But it is also the study of how to find precise locations on the planet. As it relates to the study of sea level, geodesy becomes vital. The Earth is not a perfect shape and is constantly changing. Only through a very carefully constructed system of analysis can scientists achieve the necessary accuracy about the planet's shape (the so-called 'geoid') to make measurements of sea level from space. In this animation we look at how a fleet of ground based lasers and the Global Positioning Satellite fleet contribute to a mathematically representative picture of the Earth. Note: Illusration of ground-based lasers and Global Positioning satellites measuring the shape of the Earth. Animator: Susan Twardy (HTSI), Chris Meaney (HTSI). Writer: Michael Starobin (HTSI).