Surveying
In a truly vertical photograph,

Iso-centre coincides the plumb point
Principal point coincides the isocenter
All listed here
Plumb point coincides the principal point

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Surveying
For mapping any country

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

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