hydrography
    n 1: the science of the measurement and description and mapping
         of the surface waters of the earth with special reference
         to navigation

Hydrography \Hy*drog"ra*phy\, n. [Hydro-, 1 + -graphy: cf. F.
   hydrographie.]
   1. The art of measuring and describing the sea, lakes,
      rivers, and other waters, with their phenomena.
      [1913 Webster]

   2. That branch of surveying which embraces the determination
      of the contour of the bottom of a harbor or other sheet of
      water, the depth of soundings, the position of channels
      and shoals, with the construction of charts exhibiting
      these particulars.
      [1913 Webster]