Grid length differs from geodetic length by the amount of a correction based on the ______ for the given line.

• A. average elevation
• B. scale factor
• C. forward direction
• D. back azimuth

Answer: (B)

The difference between grid length and geodetic length is governed by the projection’s scale factor along that line. Distances on a map grid are stretched or compressed relative to true ground distances by a factor k that depends on where you are and the line’s direction. So the corrected grid length is essentially the geodetic length multiplied by this scale factor: L_grid ≈ k × L_geodetic. That’s why the amount of correction is based on the scale factor for the given line. Average elevation doesn’t affect horizontal distance on a map, and while the scale factor can vary with direction, the descriptor that directly sets the amount of length distortion is the scale factor itself. For example, a true length of 1000 m with a line-scale factor of 1.001 yields a grid length of about 1001 m.