Chart Navigation & Plotting · Chart Basics
On a Mercator chart, one nautical mile is measured using the:
- ALatitude scale at the side of the chart, at the boat's approximate latitude✓ Correct
- BLongitude scale at the top or bottom of the chart
- CBar scale only, regardless of latitude
- DDistance between meridians at the equator
Explanation
One minute of latitude equals one nautical mile, so distance is read from the latitude scale on the sides. Because the Mercator latitude scale expands toward the poles, always measure at the mid-latitude of the leg, never on the longitude scale.
Authority: Bowditch, Pub. No. 9 (Mercator projection)
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