Surveying
In observations of equal precision, the most probable values of the observed quantities are those that render the sum of the squares of the residual errors a minimum, is the fundamental principle of

Gauss' Mid Latitude formula
Legendre's method
D'Alembert's method
Least square method

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Surveying
For mapping any country

Geodetic triangulation of greatest possible sides and accuracy is carried out
Primary triangles are broken down into secondary triangles of somewhat lesser accuracy
All listed here
Secondary triangles are further broken into third and fourth order triangles, the points of which are used for detail surveys

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