Geopotential meter

A geopotential meter in the gravitational field of the Earth is the vertical distance over which one must lift one kilogram of mass to increase its potential energy by 9.80665 joule. On those places on Earth where the  gravitational acceleration g  happens to be equal to 9.80665 m/s2, the geopotential meter is exactly equal to the SI meter (in this context referred to as geometric meter).

Since g depends on altitude, the geopotential meter does too. For increasing altitudes the geopotential meter becomes increasingly larger than the geometric meter, because the gravitational force weakens with altitude, with the consequence that the same amount of energy can move a kilogram over larger distances.