Parameter list

Common parameters:

+a         Semimajor radius of the ellipsoid axis
+alpha     ? Used with Oblique Mercator and possibly a few others
+b         Semiminor radius of the ellipsoid axis
+datum     Datum name (see `proj -ld`)
+ellps     Ellipsoid name (see `proj -le`)
+k         Scaling factor (old name)
+k_0       Scaling factor (new name)
+lat_0     Latitude of origin
+lat_1     Latitude of first standard parallel
+lat_2     Latitude of second standard parallel
+lat_ts    Latitude of true scale
+lon_0     Central meridian
+lonc      ? Longitude used with Oblique Mercator and possibly a few others
+nadgrids  Filename of NTv2 grid file to use for datum transforms
+no_defs   Don't use the /usr/share/proj/proj_def.dat defaults file
+pm        Alternate prime meridian (typically a city name)
+proj      Projection name (see `proj -l`)
+south     Denotes southern hemisphere UTM zone
+to_meter  Multiplier to convert map units to 1.0m
+towgs84   3 or 7 term datum transform parameters
+units     meters, US survey feet, etc.
+x_0       False easting
+y_0       False northing
+zone      UTM zone

Extended list provided by Gerald Evenden “grepped out of the RCS directory”.

+a         Semimajor radius of the ellipsoid axis
+alpha     ? Used with Oblique Mercator and possibly a few others
+azi
+b         Semiminor radius of the ellipsoid axis
+belgium
+beta
+czech
+e         Eccentricity of ellipsoid = sqrt(1 - b^2/a^2) = sqrt( f*(2-f) )
+ellps     Ellipsoid name (see `proj -le`)
+es        Eccentricity of the ellipsoid squared
+f         Flattening of the ellipsoid (often presented as an inverse, e.g. 1/298)
+gamma
+geoc
+guam
+h
+k         Scaling factor (old name)
+K
+k_0       Scaling factor (new name)
+lat_0     Latitude of origin
+lat_1     Latitude of first standard parallel
+lat_2     Latitude of second standard parallel
+lat_b
+lat_t
+lat_ts    Latitude of true scale
+lon_0     Central meridian
+lon_1
+lon_2
+lonc      ? Longitude used with Oblique Mercator and possibly a few others
+lsat
+m
+M
+n
+no_cut
+no_off
+no_rot
+ns
+o_alpha
+o_lat_1
+o_lat_2
+o_lat_c
+o_lat_p
+o_lon_1
+o_lon_2
+o_lon_c
+o_lon_p
+o_proj
+over
+p
+path
+proj      Projection name (see `proj -l`)
+q
+R
+R_a
+R_A
+rf        Reciprocal of the ellipsoid flattening term (e.g. 298)
+R_g
+R_h
+R_lat_a
+R_lat_g
+rot
+R_V
+s
+south     Denotes southern hemisphere UTM zone
+sym
+t
+theta
+tilt
+to_meter  Multiplier to convert map units to 1.0m
+units     meters, US survey feet, etc.
+vopt
+W
+westo
+x_0       False easting
+y_0       False northing
+zone      UTM zone

OGC WKT

GEOGCS["WGS 84", DATUM["WGS_1984", SPHEROID["WGS 84",6378137,298.257223563, AUTHORITY["EPSG","7030"]], TOWGS84[0,0,0,0,0,0,0], AUTHORITY["EPSG","6326"]], PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901"]], UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122"]], AUTHORITY["EPSG","4326"]]

proj4

+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs

[Unofficial] EPSG:900913 – Google Mercator 2008/Spherical

OGC WKT

PROJCS["unnamed", GEOGCS["unnamed ellipse", DATUM["unknown", SPHEROID["unnamed",6378137,0]], PRIMEM["Greenwich",0], UNIT["degree",0.0174532925199433]], PROJECTION["Mercator_2SP"], PARAMETER["standard_parallel_1",0], PARAMETER["central_meridian",0], PARAMETER["false_easting",0], PARAMETER["false_northing",0], UNIT["Meter",1], EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs"]]

proj4

+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs

EPSG:32611 – WGS84 / UTM zone 11N

OGC WKT

PROJCS["WGS 84 / UTM zone 11N", GEOGCS["WGS 84", DATUM["WGS_1984", SPHEROID["WGS 84",6378137,298.257223563, AUTHORITY["EPSG","7030"]], TOWGS84[0,0,0,0,0,0,0], AUTHORITY["EPSG","6326"]], PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901"]], UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122"]], AUTHORITY["EPSG","4326"]], PROJECTION["Transverse_Mercator"], PARAMETER["latitude_of_origin",0], PARAMETER["central_meridian",-117], PARAMETER["scale_factor",0.9996], PARAMETER["false_easting",500000], PARAMETER["false_northing",0], UNIT["metre",1, AUTHORITY["EPSG","9001"]], AUTHORITY["EPSG","32611"]]

proj4

+proj=utm +zone=11 +ellps=WGS84 +datum=WGS84 +units=m +no_defs 

EPSG:26944 – NAD83 / California zone 4

OGC WKT

PROJCS["NAD83 / California zone 4", GEOGCS["NAD83", DATUM["North_American_Datum_1983", SPHEROID["GRS 1980",6378137,298.257222101, AUTHORITY["EPSG","7019"]], AUTHORITY["EPSG","6269"]], PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901"]], UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122"]], AUTHORITY["EPSG","4269"]], PROJECTION["Lambert_Conformal_Conic_2SP"], PARAMETER["standard_parallel_1",37.25], PARAMETER["standard_parallel_2",36], PARAMETER["latitude_of_origin",35.33333333333334], PARAMETER["central_meridian",-119], PARAMETER["false_easting",2000000], PARAMETER["false_northing",500000], UNIT["metre",1, AUTHORITY["EPSG","9001"]], AUTHORITY["EPSG","26944"]]

proj4

+proj=lcc +lat_1=37.25 +lat_2=36 +lat_0=35.33333333333334 +lon_0=-119 +x_0=2000000 +y_0=500000 +ellps=GRS80 +datum=NAD83 +units=m +no_defs

EPSG:26965 – NAD83 / Hawaii zone 5

OGC WKT

PROJCS["NAD83 / Hawaii zone 5", GEOGCS["NAD83", DATUM["North_American_Datum_1983", SPHEROID["GRS 1980",6378137,298.257222101, AUTHORITY["EPSG","7019"]], AUTHORITY["EPSG","6269"]], PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901"]], UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122"]], AUTHORITY["EPSG","4269"]], PROJECTION["Transverse_Mercator"], PARAMETER["latitude_of_origin",21.66666666666667], PARAMETER["central_meridian",-160.1666666666667], PARAMETER["scale_factor",1], PARAMETER["false_easting",500000], PARAMETER["false_northing",0], UNIT["metre",1, AUTHORITY["EPSG","9001"]], AUTHORITY["EPSG","26965"]]

proj4

+proj=tmerc +lat_0=21.66666666666667 +lon_0=-160.1666666666667 +k=1.000000 +x_0=500000 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs

EPSG:4135 – Old Hawaiian

OGC WKT

GEOGCS["Old Hawaiian", DATUM["Old_Hawaiian", SPHEROID["Clarke 1866",6378206.4,294.9786982138982, AUTHORITY["EPSG","7008"]], AUTHORITY["EPSG","6135"]], PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901"]], UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122"]], AUTHORITY["EPSG","4135"]]

proj4

+proj=longlat +ellps=clrk66 +no_defs