Produce a basemap for the figure.
Several map projections are available, and the user may specify separate tick-mark intervals for boundary annotation, ticking, and [optionally] gridlines. A simple map scale or directional rose may also be plotted.
At least one of the options B, L, or T must be specified.
Full option list at https://www.generic-mapping-tools.org/gmt/latest/basemap.html
B = frame
J = projection
R = region
J (str) – Required if this is the first plot command. Select map projection.
L (str) –
'[g|j|J|n|x]refpoint'Draws a simple map scale centered on the reference point specified.
Td (str) – Draws a map directional rose on the map at the location defined by the reference and anchor points.
Tm (str) – Draws a map magnetic rose on the map at the location defined by the reference and anchor points