Good ideas here.

I've always wanted to be able to draw my horizon in Guide, and have it
save it to a horizon file for me. A panorama picture would have been a
nice feature too, but one ought to be able to use it to trace the
ground, buildings etc. My common observing sites all have obstructions
that go high up in the sky (indeed, observing from a balcony even
precludes views of the zenith).

As for grouping marks in categories, I'd suggest you just create a
suggested number of groups, and allow the user to edit these and
create their own. Creating a set of categories to please everybody is
just not going to happen.

Regards,

Arild :)