I normally pre-plan, but may decide to stray from the route if I see something interesting, have the energy and weather is suitable. Sometimes in the hills it is useful to have a wider view to identify where there may be hazards to avoid or to plot an escape route if the weather deteriorates. I suppose each of these, except choosing to leave the route, would be plantable in advance. I think I would probably also carry a map and compass. This would be a backup to the GPS and give me the option of a wider view of the area. I don’t yet have a GPS and have not used one, so I don’t really know how much of the map I could see on one.