Using Command-Line Tools - Desktop GIS: Mapping the Planet with Open Source Tools - page 166

-Jd|D<lon0>/<lat0>/<lat1>/<lat2>/<scale|mapwidth> (Equidistant Conic)
-Je|E<lon0>/<lat0>/<scale (or radius/lat)|mapwidth>

(Azimuthal

Equidistant)
-Jf|F<lon0>/<lat0>/<horizon>/<scale (or radius/lat)|mapwidth> (Gnomonic)

-Jg|G<lon0>/<lat0>/<scale (or radius/lat)|mapwidth> (Orthographic)

-Jh|H<lon0>/<scale|mapwidth> (Hammer-Aitoff)
-Ji|I<lon0>/<scale|mapwidth> (Sinusoidal)
-Jj|J<lon0>/<scale|mapwidth> (Miller)
-Jk|K[f|s]<lon0>/<scale/mapwidth> (Eckert IV (f) or VI (s))
-Jl|L<lon0>/<lat0>/<lat1>/<lat2>/<scale|mapwidth> (Lambert Conformal
Conic)
-Jm|M (Mercator). Specify one of two definitions:
-Jm|M<scale|mapwidth>
-Jm|M<lon0>/<lat0>/<scale|mapwidth>
-Jn|N<lon0>/<scale|mapwidth> (Robinson projection)
-Jo|O (Oblique Mercator). Specify one of three definitions:
-Jo|Oa<orig_lon>/<orig_lat>/<azimuth>/<scale|mapwidth>
-Jo|Ob<orig_lon>/<orig_lat>/<b_lon>/<b_lat>/<scale|mapwidth>
-Jo|Oc<orig_lon>/<orig_lat>/<pole_lon>/<pole_lat>/<scale|mapwidth>
-Jq|Q<lon0>/<scale|mapwidth> (Equidistant Cylindrical)
-Jr|R<lon0>/<scale|mapwidth> (Winkel Tripel)
-Js|S<lon0>/<lat0>/[<slat>/]<scale (or radius/lat)|mapwidth>
(Stereographic)
-Jt|T (Transverse Mercator). Specify one of two definitions:
-Jt|T<lon0>/<scale|mapwidth>
-Jt|T<lon0>/<lat0>/<scale|mapwidth>
-Ju|U<zone>/<scale|mapwidth> (UTM)
-Jv|V<lon0>/<scale/mapwidth> (van der Grinten)
-Jw|W<lon0>/<scale|mapwidth> (Mollweide)
-Jy|Y<lon0>/<lats>/<scale|mapwidth> (Cylindrical Equal-area)
-Jp|P[a]<scale|mapwidth>[/<origin>] (Polar [azimuth] (theta,radius))
-Jx|X<x-scale|mapwidth>[l|p<power>][/<y-scale|mapheight>[l|p<power>]]
(Linear projections)
(See psbasemap for more details on projection syntax)

Each projection requires different parameters. In our example we used
-JA0/20/4.5i . This selects the projection (Lambert Azimuthal Equal Area)
and sets the longitude to 0 degrees, the latitude to 20 degrees, and
the width of the map to 4.5 inches. Note that either -J or -j can be
used. Specifying uppercase indicates that the last parameter (in our
case 4.5i) is width. Had we used a lowercase j, GMT would interpret the
last parameter as a scale value. Widths can be specified using c , i , p , or
m , which correspond to centimeters, inches, points (1/72 of an inch),
and meters.

You can quickly see two things:

• GMT has a lot of options.

• You might want to read the manual.