So as I understand, rhumblines are useful for doing simple navigation where you care about keeping things simple and always moving at the same direction according to a compass. Useful for navigating in times before the GPS. Recently I was talking with someone about a fantasy setting that is a flat world and where the compasses point towards the world's centre. Then I remembered someone did create a world map that included rhumblines: But thinking about it, the rhumblines in that world would probably be different based on how those compasses work. It would probably be something closer to operating on polar coordinates or something. So, how would you draw more setting-accurate rhumblines with the way that world operates? What would be the useful way for navigators to operate?