Preview images: spacing of 5 arcsec may need to be adjusted.
Currently, I'm setting 5 arcsec for the grids to make it less crowded. But when the extents are less than or between the 5ths, the labels don't show up, e.g. the Longitude labels for the following plot.
Will need to add a check to see if the labels are displayed, and if not then to adjust the spacing.