How fast the point beneath a Body moves over the ground, along the local north and east at that point, in kilometres a second: what the Course is the direction of, and what a map can carry a marker along between the instants it propagates.
How fast the point beneath a Body moves over the ground, along the local north and east at that point, in kilometres a second: what the Course is the direction of, and what a map can carry a marker along between the instants it propagates.