Great work, runs very smoothly! Where do you do the shadow calculation? Do you have precomputed tilesets or do you do it on the client?
It also takes into account the Earth's curvature, so you can zoom out to planet level and it still works.
By the way, you might like https://felixpalmer.github.io/volcanoes-of-japan/
Great link, thanks. Horizontal scrollbar tripped me out a little bit though...