iPad won't download some areas

Yosemite, Jtree, Eastern Sierra
The little download wheel is spinning,but it doesn't seem to make any progress.
I have tried leaving the app open.

Other areas seem to download fine, even while these are stalling.

Any ideas?

Kill the app and restart it. You might be downloaded too many GIANT areas at once. Try one at a time. If all else fails, delete the app from the phone and reinstall it from the store - that completely clears everything.