Reads the nearest selected link or path within range: how far away it is, how far along it, a value blended between its ends, or its change per horizontal block. Roads and rivers carve with this.
One of: Distance, Position along (0 to 1), Distance along, Value blended between ends, End value change per horizontal block, Direction (0 undirected, 1 first to second, 2 second to first, 3 both), Upstream value, Downstream value, Downstream position (0 to 1), Link value.