GMT programs that read position data will need to know how to convert the input coordinates to positions on the map. This is achieved by selecting one of several projections. The purpose of this section is to summarize the properties of map projections available in GMT, what parameters define them, and demonstrate how they are used to create simple basemaps. We will mostly be using the pscoast command and occasionally psxy. (Our illustrations may differ from yours because of different settings in our .gmtdefaults file.) Note that while we will specify dimensions in inches (by appending i), you may want to use cm (c), meters (m), or points (p) as unit instead (see gmtdefaults man page).
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Coordinates (-–Jp -–JP)