Trigonometry is a branch of mathematics that developed from simple mensuration.

Trigonometry is a branch of mathematics that developed from simple mensuration (measurement of geometric quantities), geometry, and surveying. In its modern form it makes use of concepts from algebra and analysis. Initially it involved the mathematics of practical problems, such as construction and land measurement; it has since been extended to the geometry of three-dimensional spaces in the form of SPHERICAL TRIGONOMETRY. This article, however, will deal only with plane trigonometry.
Land survey makes use of the process of triangulation, in which a chosen network of triangles is measured. In pure triangulation, a base line to one triangle is measured, and the rest of the survey involves measuring angles only; in mixed triangulation, certain sides and angles are measured; in chain triangulation, only sides are measured.