Answer: triangulation

AnswerCrossword Clue
triangulation(in surveying) The tracing and measurement of a series or network of triangles in order to determine the distances and relative positions of points spread over a territory or region, esp. by measuring the length of one side of each triangle and deducing its angles and the length of the other two sides by observation from this baseline
triangulationFormation of or division into triangles
triangulationin geology, a method of locating an epicenter by determining how far it lies from three widely separated seismographs