3d maps load order is glitchy

[rafaqz]

Its common to get large white areas randomly in the middle, while very distant tiles loaded straight away:

Sometimes these white gaps linger for ages. This is from the 3d maps example in the docs. And this isn't simply randomness in download times, the further tiles are be scheduled first.

[rafaqz]

Another from the docs. Here a few non-contiguous patches of point cloud loaded