hypsometry

n. science that deals with elevations and altitudes measurement, hypsography, branch of geography that deals with the mapping and measurement of high places

Hypsometry is the measurement of land elevation relative to sea level.
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Noun
1. measurement of the elevation of land above sea level
(synonym) hypsography
(hypernym) measurement, measuring, measure, mensuration

(n.)
That branch of the science of geodesy which has to do with the measurement of heights, either absolutely with reference to the sea level, or relatively.
  

Science or art of determining terrain relief, by any method.