[cartography]
The direction line drawn on a map from the known position of a distant feature back to the viewer's position; a line from the viewer's current position backward along a route; the opposite direction from a given azimuth calculated by adding 180 degrees to azimuths less than 180 degrees or subtracting 180 degrees from azimuths greater than 180 degrees. Also known as a backsight or a direction line.