If you want to tear the bottom out of a ship, you can set a course that ignores shoal water and rocks, and attempt to sail straight through. Marine GPS systems don’t follow navigation “roads”. You need to manually program in way points that can be traveled to in a straight line. (And you have to set the way points a bit “off” the channel markers, or you’ll run into them.)
Apple is using GPS in iPhones for location-based reminders. So you can create a reminder to call your wife when you leave work, and your iPhone creates a “geofence” around your work, which triggers the reminder alert once you cross the geode center threshold. Pretty nifty.