This is a very specific problem with Generic Mapping Tools which I didn’t find well documented: if you map certain symbols to a list of coordinates specified in COORDINATES.xy, you can specify that subsets of those coordinates are mapped to symbols in different colors in two ways:
- You add a column containing numerical values that map to colors in
COLORS.cpt. This option is illustrated in my earlier post on making WALS maps. - You add coloring instructions directly to your
COORDINATES.xyfile by adding a line such as> -Gred. The hard-to-find part here was the fact that you need to prefix the color option by>.
In this case, your COORDINATES.xy file might look like this:
8.74, 9.72 11.80, 29.28 -8.65, 141.52 66.40, 17.43 70.67, 130.91 -29.71, 19.08 43.50, -88.50 -2.91, -68.91 42.04, 43.99 -10.61, 150.73 > -Gwhite -Wblack 56.80, -120.35 -13.81, -65.63 7.60, 6.04 > -Ggray -Wblack -16.27, 168.01 -16.17, 168.14 -16.31, 168.05 -17.70, 168.38 -15.43, 167.24
You can then use this file, for example, with the following commands to produce a world map displaying these coordinates:
pscoast -R-20/340/-70/80 -Dl -A100/0/1 -JQ9.5i -W -B -K > MAP.ps psxy COORDINATES.xy -R -J -O -Sc0.25c -i2,1 -Gblack >> MAP.ps
The result looks like this:
