True, and countries that are empty except for random river squiggles can save a good bit of storage (at the highest zooms so those river squiggles are isolated)

True, and countries that are empty except for random river squiggles can save a good bit of storage (at the highest zooms so those river squiggles are isolated), but, again, if you have to start with the lowest level first, the described approach isn't saving a whole lot in processing time, even with big empty space. One thing I forgot to say in my top post, though, is the presentation mentions compositing layers together on the fly, and that is one of the key tools they use, but the presentation drops that thread. I'm curious if originally it had more on that front and what they do with that.