Margins are the start and end points of a journey and are typically characterised by geography. For example nautical coastlines are commonly used as margins having both aesthetic and historical value (they are the traditional start and end points of early ship-based expeditions).
Once applied to a Path, Margins reveal the prime intent of a journey's route.
Each geographical region has different types of Margins.
Journeys outside the polar regions should use the most appropriate margin type for the area.