Altitude is defined as: "The height of anything above a given planetary reference plane, especially above sea level on earth". So what is sea level and how is it calculated? Check out this great minute physics video and see various altitude related info here.
Highlights from the video:
- The summit of Chimborazo, in Ecuador, is the furthest point from the center of the earth. Not Everest.
- Geodesists created the World Gravitational Model to predict the average seal level within a meter anywhere on earth which is used in GPS devices and is the basis for the actual height of mountains on the earth.
Mount Everest, at 29,035 feet, is the highest point on the planet.
Chimborazo, at 20,560 feet and less than 1 degree south of the equator in Ecuador, is the furthest point from the center of the earth.