In order to estabish plans with satistactory precision, it was absolutely necessary to determione throughout the territory a certain number of clearly visibvle points which would serve as support for current topographical measurements.
In France, IGN. opted for the LAMBERT system (conical projection) thus creating a LAMBERT grid.
This grid makes it possible to designate all these points by their rectangular coordinates ( Y , Y ). To avoid excessive deformations, France is divided into four zones :
In France there are nearly 100,000 points making up the geodetic network. They are all visible from each other, and are therfore located high up. All shese points are marked on notebooks and data sheet are made available 
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