In Geodesy
Instead of using the sea level, geodesists often prefer to define height from the surface of a reference ellipsoid, see Geodetic system, vertical datum.
Defining the height of geographic landmarks becomes a question of reference. For example, the highest mountain by elevation in reference to sea level belongs to Mount Everest, located on the border of Nepal and Tibet, China; however the highest mountain by measurement of apex to base belongs to Mauna Kea in Hawaii, United States.
Read more about this topic: Height