USCG Exam Practice · Plot true course and distance between two charted points
When measuring the distance between two charted points on a Mercator chart, where must you apply the dividers to the latitude scale?
- AAt the equator, where the scale is most accurate
- BAt the top of the chart for maximum precision
- CAt the mean latitude of the line being measured✓ correct
- DAt any convenient latitude since the scale is uniform
Why C is correct
Bowditch Ch. 4 §402 states that distances must be measured at the latitude of the line because meridian length varies with latitude on a Mercator projection. Using the wrong latitude introduces measurement error.
Cited:Bowditch Ch. 4 §402
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