ER

 Projection     : Equirectangular
 Also known as  : Equidistant Cylindrical, Simple Cylindrical,
                  Rectangular, or Plate Carree
 General class  : cylindrical
 Characteristics: neither equal-area nor conformal
 Earth model    : sphere

Defining the MAPUNITS:

 MapUnits "er"       ! Standard name
 MapUnits "er e19"   ! 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:

 E100, "Invalid data" - In converting from projection coordinates 
        to geographic coordinates, there was an input data error