Chart Navigation & Plotting · Mercator Projection
On a Mercator chart, distance is measured using the:
- ALongitude scale at the top or bottom border
- BLatitude scale at the side border, abreast of the area being measured✓ Correct
- CCompass rose
- DBar scale only, regardless of latitude
Explanation
Because the Mercator latitude scale expands toward the poles, distance must be measured on the latitude (side) scale at the same latitude as the line being measured. One minute of latitude equals one nautical mile. The longitude scale must never be used for distance.
Authority: Bowditch, American Practical Navigator (Pub. 9), Mercator chart use
Practice the full Chart Navigation & Plotting bank
Free spaced-repetition quizzing across 2190 USCG exam questions — it schedules your reviews so the ones you miss come back until they stick.
Related Chart Navigation & Plotting questions
- Mercator Projection
On a Mercator chart, a rhumb line (line of constant course) appears as:
- Chart Basics
On a Mercator chart, one nautical mile is measured using the:
- Chart Basics
The principal advantage of the Mercator projection for navigation is that:
- Chart Basics
Charted depths (soundings) on a U.S. chart are referenced to which tidal datum?
- Chart Basics
Vertical clearances of bridges and overhead cables on a U.S. chart are normally referenced to:
- Distance, Speed & Time
A vessel makes good 12 knots. How far does it travel in 20 minutes?