Air, land, and sea routes
Airplane, helicopter, train, boat, line, and dots draw a great-circle arc between the two stops. That is the right look for a flight or a ferry when you do not have a track.
Car, bus, motorcycle, tuk-tuk, and camper ask a driving router for the road shape. Bicycle and walking use bike and foot profiles. If the router cannot connect two points — an ocean in between is the usual reason — the leg falls back to an arc.
You can mix modes. Fly into a city, then drive the next leg, then take a boat. Each leg keeps its own icon, and that icon rides the front of the line while the leg is animating.
A dotted leg draws the path without a vehicle. A plain line does the same with a solid stroke.