I’d really appreciate if the grayed out PNG write option would be filled with life 
It’s a wide-spread format, suitable for height fields, patent-free, good compression,
very easy to implement (especially if you don’t need the fancy bits, basically you
never need to write anything except raw 16-bit gray values). Also, there is a free
implementation available for commercial use: http://www.libpng.org/
Some other points (played around with it a bit after purchasing the Standard Edition):
I think it would make more sense to use the same executable for all editions and
just unlock features after entering the purchase key. Not much point in downloading
and reinstalling basically the same app (most purchasers will have tried Basic). This also
avoid the hassle when someones download fails during purchase. And when your
program becomes popular enough to attract the attention of hackers, they will
find a way to get their hands on a non-Basic executable anyway.
As you already keep track of the “modified” state of the terrain, it would be customary
to indicate that state by appending an asterix (*) to the file name in the title bar.
Considering that this forum explicitely offers to “Hide E-Mail from Public”,
I did wonder why I see an icon “Send E-Mail to” next to my posts :roll: