While the Cartesian linear projection is primarily designed for regular floating point x,y data, it is sometimes necessary to plot geographical data in a linear projection. This poses a problem since longitudes have a 360 periodicity. GMT therefore needs to be informed that it has been given geographical data allthough a linear transformation has been chosen. We do so by appending a d (for degrees) to the end of the -Jx (or -JX) option. As an example, we want to plot a crude world map centered on 125E. Our command will be
gmtset GRID_CROSS_SIZE_PRIMARY 0.1i BASEMAP_TYPE FANCY PLOT_DEGREE_FORMAT ddd:mm:ssF pscoast -R-55/305/-90/90 -Jx0.014id -B60g30f15/30g30f15WSen -Dc -A1000 -Glightgray -W0.25p -P \ > GMT_linear_d.ps gmtset GRID_CROSS_SIZE_PRIMARY 0
with the result reproduced in Figure 5.2.