A projection requires a set of parameters that are used to convert between latitude and longitude and easting and northing. These parameters can be found in the EPSG geodetic parameter database.
For a Transverse Mercator projection and a Lambert Conformal Conic projection these are respectively:
The geographic origin is the intersection of the central meridian with the latitude of the origin. The projection origin values at that point are the false easting and false northing. The reason for the high positive values for these parameters where applicable, is to avoid negative values. In both cases above this is for the easting but is not necessary for the northings which are both ‘0’, as the projection is not intended for use south of the origin.
There are several other types of projection, most of which are of more interest to cartographers than having any application in E&P.
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