Drawing and Labelling Parallels and Meridians

Most maps include a graticule grid, a reference network of labelled latitude and longitude lines. Basemap does this with the :func:`~mpl_toolkits.basemap.Basemap.drawparallels` and :func:`~mpl_toolkits.basemap.Basemap.drawmeridians` instance methods. The longitude and latitude lines can be labelled where they intersect the map projection boundary. There are four exceptions: meridians and parallels cannot be labelled on maps with proj set to ortho (orthographic) or vandg (van der Grinten), and meridians cannot be labelled on maps with proj set to robin (robinson), mbtfpq (McBryde-Thomas Flat Polar Quartic), moll (mollweide) or sinu (sinusoidal). This is because the lines can be very close together where they intersect the boundary on these maps, so that they really need to be labelled manually on the interior of the plot.