Your question doesn't make any sense.
"How far can you see?", and "how far away is the horizon?", are two completely different questions.
The horizon line is the same distance for folks at the same altitude at any point on the same planet.
You can only see a few hundred yards in downtown manhatten because buildings block your view of everything beyond, including the horizon. Same with being in "Sherwood Forest", or the Amazon jungle, except its trees instead of buildings blocking your view.
If your question is about "visibility" (how far an airplane pilot can see at a given moment) then that changes with the local weather, and that data is also included in the weather forecasts each day. But that has nothing to do with where the horizon is to the viewer.
The horizon changes with your altitude. The guy in the ships crows nest on top of the mast has a more distant horizon than the people on deck. But if the ship is in thick fog both are likely to have the same short distance of visibility.