I liked the idea behind the gsp subfunction, and it *is* much more efficient than scatter. I tried this section on its own. But it should be used with care - the order that you work through the colormap will affect the final plot, with later (default red) colours overlaid over earlier (default blue) wherever the dots are crowded close together. Especially if you shrink the figure this can result in a massive bias towards (default) red. To test the effect on your plot, try replacing the loop with
Very useful, thanks. The help suggests using AXIS(AXIS) to fix the limits, I think the same effect can be acheived with AXIS MANUAL, which would be clearer.
It's also not obvious that the arrow will be a patch object, so has properties like edgecolor, facecolor, rather than line properties.