On a chart based on a Mercator projection, a straight line is

• A. A great circle
• B. the shortest distance between 2 points
• C. a rhumb line
• D. varies in track depending on your location on earth

Answer: (C)

On a Mercator projection, a line drawn straight on the chart represents a rhumb line, which is a path of constant bearing. This happens because Mercator preserves angles, so a path that crosses all meridians at the same angle shows up as a straight line on the map. A rhumb line keeps the same bearing as you travel, unlike a great circle—the true shortest distance between two points on the globe—which generally appears curved on a Mercator chart. Since the straight line on the chart corresponds to constant bearing, its track doesn’t vary with location along the route.