usage: http://jules.unavco.org/Gmthelp/gmt_region?e=-120&n=-80&de=5&dn=5

central point: -120.00000000000 E -80.00000000000 N
nominal half-widths: 5.00000000000 x 5.00000000000 great-circle degrees

GMT lower-left: -165.10870083980 E -82.94686216882 N
GMT upper-right: -101.36723468433 E -74.20070924158 N

-R-165.10870083980/-82.94686216882/-101.36723468433/-74.20070924158r