You put in the coordinates of where you want to go. Then you start out on the journey. If you stray from the course, the GPS recalibrates the direction you should go. When I didn't, it told me it would recalibrate the route. This is the way mappers do as opposed to planners who feel they need to follow the plan.
Mappers have a destination in mind.
How they get their is unimportant as long as they get their and their journey is repeatable by others.