I made minimal changes to my copy of basemap to support the new quiver and quiverkey, and to illustrate them in quiver_demo.py. The older quiver is still accessible as quiver_classic. A diff against svn is attached. (It includes do-nothing diffs caused by my editor's deletion of end-of-line whitespace when a file is saved.) If you like, I can commit the changes.
There is still what I hope is a minor flaw: when the aspect ratio is controlled, as in basemap, it seems that the changes in rendered arrow width upon zooming are a bit jumpy, and the key arrow width can end up a bit different from the map arrow widths. I don't think this affects the length, so the key is still valid (as far as I have been able to determine.) I would like to improve this, but I don't think that use of the new quiver needs to wait for it.
bm.diff (10.4 KB)