unless you're going in a straight line to a landmark, obviously that's all discovered.
Quoted for truth!
If you simply auto-route-plot a course from the bubble to one nebula, to the next nebula, to major black holes, etc, etc then the chances are that you won't hit any undiscovered worlds. This is because these are the same routes that everyone else has taken.
[video=youtube_share;TBD7txMVbxs]https://youtu.be/TBD7txMVbxs[/video]
It's easy to get fooled into thinking that everything's already been discovered. It really REALLY hasn't. Only a tiny TINY fraction of the galaxy has been explored.
If you're making a trip out to a nebula or something then start your trip by picking a random direction away from all the obvious stuff. Head out for around 200LY and then turn towards your tourist detination. You should find (unless you're unlucky) that you will be able to claim many new undiscovered worlds along the way.