What is the rate of change in latitude per year, in centimeters, for the PRS92 station ZGN-6 between 1990 and 2010?

• A. 11.7
• B. 10.7
• C. 12.7
• D. 9.7

Answer: (A)

The rate in centimeters per year is simply how far north–south the station moves on the ground each year. To get it, you take the total change in latitude from 1990 to 2010, convert that angular change into a ground distance, and divide by the 20-year interval.

If the station moves about 2.34 meters overall in that 20-year span, then per year it moves 2.34 m / 20 = 0.117 m/year, which is 11.7 cm/year. That's why 11.7 cm/year is the correct value for the latitude rate in this case.

In practical terms, latitude changes translate to a north–south displacement on the Earth’s surface roughly by 111.32 km per degree of latitude, so the same calculation can be done by converting the latitude difference to ground distance first, then dividing by the number of years.