Triangulation Maps and Trig Points

TriangulationMapOfStatenIsland_1851

Triangulation maps, computing distances between known points, were used for ship navigation. Above is a triangulation map of Staten Island, below of the south-east quadrilateral of India (super-high res version here).

PrincipalTriangulationOfSEQuadrilateralOfGTSOfIndia_1878-web

Known positions with carefully measured latitude/longitude and altitude are called “trig points”, and are often marked, sometimes with a metal plate or, in the case of this marker in New Zealand, an amazing sculptural tower.

MountJohnNZ_TrigPoint-web