Gemma Frisius (1508–1555), Frisian mathematician, cartographer and instrument maker
Primarily, a 1536 globe of cartographer Gemma Frisius depicts an area within the Arctic Circle, north of a strait dividing Terra Corterealis and Baccalearum Regio from the westward projection of Greenland.
The Dutch scientist Gemma Frisius was the first to propose the use of a chronometer to determine longitude in 1530.
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Triangulation, as invented by Gemma Frisius around 1533, consists of making such direction plots of the surrounding landscape from two separate standpoints.