6.2.1.1 Rectangular map

In this mode we define our region by specifying the longitude/latitude of the lower left and upper right corners instead of the usual west, east, south, north boundaries. The reason for specifying our area this way is that for this and many other projections, lines of equal longitude and latitude are not straight lines and are thus poor choices for map boundaries. Instead we require that the map boundaries be rectangular by defining the corners of a rectangular map boundary. Using 0$^{o}$E/40$^{o}$S (lower left) and 60$^{o}$E/10$^{o}$S (upper right) as our corners we try

gmtset PLOT_DEGREE_FORMAT ddd:mm:ssF GRID_CROSS_SIZE_PRIMARY 0
pscoast -R0/-40/60/-10r -JA30/-30/4.5i -B30g30/15g15 -Dl -A500 -Glightgray -W0.25p -P > \
    GMT_lambert_az_rect.ps

Figure 6.4: Rectangular map using the Lambert azimuthal equal-area projection.

Note that an ``r'' is appended to the -R option to inform GMT that the region has been selected using the rectangle technique, otherwise it would try to decode the values as west, east, south, north and report an error since 'east' $<$ 'west'.