🔍 Key Concepts

• Great circle tracks on a gnomonic chart and how they appear when transferred to a Mercator chart • The definition of the vertex of a great circle (highest latitude point) and where it typically lies between two North Atlantic ports • How distance on a great circle route is actually measured and what latitude you use

💭 Think About

• Sketch (even roughly) the great circle between Cape Race (46°30'N, 53°00'W) and Reykjavik (~64°N, 22°W) on a North Atlantic chart. Where would you expect the highest latitude point to be relative to Reykjavik and Cape Farewell? • Think about how great circles appear on a Mercator chart in the Northern Hemisphere: does the curve bow toward or away from the pole? How would that look relative to Cape Farewell? • Review how you normally measure great-circle distance after laying it out on a gnomonic chart. Do you use one single mid-latitude for the whole route, or segment-by-segment on a Mercator chart?

✅ Before You Answer

• Verify the definition of vertex: it is the point of maximum latitude on the great circle, not necessarily at either terminus. • Check on a Mercator chart whether a great-circle track in the North Atlantic between Newfoundland and Iceland is concave toward or away from the North Pole. • Confirm whether correct distance practice is to use one mid-latitude degree length for the entire track, or to transfer the track in segments to a Mercator and measure each segment separately.