Navigation General · Chart Datums & Projections
A gnomonic chart is primarily used for which purpose?
- APlotting radar ranges and bearings in coastal waters
- BPlotting great-circle routes, then transferring waypoints to a Mercator chart✓ Correct
- CMeasuring rhumb-line distances with a parallel ruler
- DDisplaying tidal current vectors in estuaries
Explanation
On a gnomonic projection, great circles plot as straight lines, making it ideal for planning the most efficient ocean route. Because the gnomonic is not conformal and distances are hard to measure directly, navigators transfer the great-circle waypoints to a Mercator chart for actual course-line plotting.
Authority: Bowditch (Pub. 9), Ch. 2
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