Chart Navigation & Plotting · Chart Basics — Latitude Scale for Distance
On a Mercator chart, distance is always measured using:
- AThe compass rose diameter
- BThe longitude scale along the top and bottom borders
- CAny convenient part of the latitude scale
- DThe latitude scale (side border) at the same latitude as the area being measured✓ Correct
Explanation
On a Mercator projection the latitude scale expands toward the poles, so one minute of latitude (= one nautical mile) must be taken from the side border at the same latitude as the line being measured. The longitude (bottom/top) scale must never be used for distance.
Authority: Bowditch (Pub. No. 9); Chart No. 1
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
- 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?
- Distance, Speed & Time
A vessel covers 9 nautical miles in 45 minutes. What is its speed?