Which term describes the bearing measured from north in the reverse direction of a line, as used in grid length corrections?

• A. Back azimuth
• B. Scale factor
• C. Forward direction
• D. Average elevation

Answer: (A)

A line has two directions, so there’s a bearing for each way along it. The term that describes the bearing measured from north in the reverse direction of the line is back azimuth. This is the direction from the far end back toward the near end, which is why it’s used in grid length corrections: you often need the orientation of the line when you’re moving from one endpoint to the other and applying adjustments that depend on direction.

If you know the forward azimuth (the bearing from the starting point to the ending point), the back azimuth is simply that angle plus 180 degrees (mod 360). For example, a forward azimuth of 30 degrees corresponds to a back azimuth of 210 degrees.

The other terms mentioned are not about the reverse direction: scale factor is about converting grid distances to ground distances, and average elevation is unrelated to bearing.