Source : Webster's Revised Unabridged Dictionary (1913)

Triangulation \Tri*an`gu*la"tion\, n. [Cf. F. triangulation.]
   (Surv.)
   The series or network of triangles into which the face of a
   country, or any portion of it, is divided in a
   trigonometrical survey; the operation of measuring the
   elements necessary to determine the triangles into which the
   country to be surveyed is supposed to be divided, and thus to
   fix the positions and distances of the several points
   connected by them.

Source : WordNet®

triangulation
     n 1: a trigonometric method of determining the position of a
          fixed point from the angles to it from two fixed points
          a known distance apart; useful in navigation
     2: a method of surveying; the area is divided into triangles
        and the length of one side and its angles with the other
        two are measured, then the lengths of the other sides can
        be calculated