USCG Exam PracticePlot true course and distance between two charted points
When measuring the distance between two charted points on a Mercator chart, where must the dividers be placed on the latitude scale?
- A. At the equator, where the scale is most accurate
- B. At the top of the chart for consistency
- ✓ At the mean latitude of the line being measuredCorrect
- D. At the longitude of the departure point
Why C is correct
Bowditch Ch. 4 §402 states that distances must be measured at the latitude of the line, since meridian length varies with latitude on a Mercator projection. Using the equator or any other latitude will introduce error.
Cited:Bowditch Ch. 4 §402