The invention is a new and useful improvement to navigation system software that, when combined with conventional navigation system hardware, provides an operator with a means for modifying a course generated by a navigation system, and for saving the modified course for future trips. More specifically, the invention comprises an improvement to navigation system software that provides several manual means for modifying a computer-planned course according to real-time operator preferences; and an improvement to navigation system software that provides an automatic means for adapting navigation system planning to conform to a course that an operator has used repetitively.