A common use case (for me) is this:
A group of geocachers are out on a trip. They have a pre-compiled GPX file created via Project-GC or Geocaching.com. This contains all geocaches that they want to log during the trip. I myself might have an agenda of my own as well. That agenda might include geocaches that I would like to log, but aren't too important to the others. A new D/T combo for myself, a challenge, or something that others has already logged. If we are passing close enough to them it might be worth the extra stop.
This is why I would like to be able to use more than one offline database simultaneously. I can then have the "group list" enabled, and also at the same time see for example "my own needed D/T".
I would like the cache icons to have some form of indicator showing that they are from different lists, so that I can easily see which ones are the groups main goal. It could be color coding by adding circles around the cache icons or a small number in a corner.
In my opinion, 3-5 simultaneous lists should be enough. The first one selected of them is the most important to visually stick out from the others.
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