This map extract shows exact heights by a black dot with a number next to it. The number is the height above sea level in metres. The blue triangle represents a triangulation pillar; the networks ...

And so you can actually make a map of where that value of gravity times height is under the continent. And that becomes, quote, the new sea level.” ...

An analysis of the map additionally led to the discovery of a number of previously unknown mountains, the tallest of which stands no higher than 700 m (2,297 ft) above the surface.

Height above sea level is both a simple and a complex concept. At the simple level, the height of a sea wall can easily be measured as so many metres above the apparently flat surface of a calm sea.