MER

 Projection     : Mercator
 General class  : cylindrical
 Characteristics: conformal
 Earth model    : ellipsoid or sphere

Defining the MAPUNITS:

 MapUnits "mer"      ! Standard name
 MapUnits "mer e0"   ! Standard name and ellipsoid

Other parameters:

 TrueOriginLongitude "central_meridian"        ! Required, for True origin
 TrueOriginLatitude  "latitude_of_true_scale"  ! Required, for True origin
 FalseEasting        "false_easting"           ! Optional, default is zero
 FalseNorthing       "false_northing"          ! Optional, default is zero

Possible errors:

 E334, "Point cannot be projected" - In converting from geographic 
        coordinates to projection coordinates, the transform cannot 
        be computed at the poles.