BUG: Program is too eager to please with aerial photos, generating
excessive network traffic, disk space usage, and load on terraserver,
and sometimes the program seems non-responsive as a result.
Zooming in/out or panning seems to trigger downloads. Even accidental
zooms from mouse wheel.
Restarting the program triggers aerial photo downloads for Jefferson, GA
View -> aerial photos should be interpreted as show them if they
are already loaded. A separate button on the left toolbar should be used
to actually initiate downloads.