The Collaborative International Dictionary of English v.0.48:

Hypsometry \Hyp*som"e*try\, 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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hypsometry
    n 1: measurement of the elevation of land above sea level [syn:
         hypsometry, hypsography]