Which statement correctly compares the scale factors at the origin of PTM Zones and UTM Zones?

• A. The scale factor at the origin of any PTM Zone is greater than the scale factor of any UTM Zone by 0.00035.
• B. The scale factor at the origin of any PTM Zone is lesser than the scale factor of any UTM Zone by 0.0035.
• C. The scale factor at the origin of any PTM Zone is lesser than the scale factor of any UTM Zone by 0.00035.
• D. The scale factor at the origin of any PTM Zone is greater than the scale factor of any UTM Zone by 0.0035.

Answer: (C)

The main idea is the scale factor at the origin, which is the local expansion or contraction along the central line of a projection. For UTM, the central meridian is defined with a scale factor of 0.9996 to minimize distortion within each zone. PTM zones use a slightly smaller central scale factor, specifically 0.00035 less than the UTM value, so the PTM origin scale factor is 0.9996 − 0.00035 = 0.99925. That means the PTM origin is smaller than the UTM origin by 0.00035, which is why this option is the best match.