On a standard Mercator map, a line of constant bearing on the Earth appears as what?

• A. Straight line
• B. Curve
• C. Circle
• D. Spiral

Answer: (A)

Lines of constant bearing, or rhumb lines, map to straight lines on a Mercator chart because the projection preserves angles. In Mercator, meridians are drawn as vertical lines and the chart is designed so that the angle a path makes with those meridians stays the same when projected. So if you steer with a fixed heading relative to north, that constant angle becomes a straight line on the map, making navigation straightforward. By contrast, a great-circle route—the shortest path on the globe—often appears as a curve on Mercator maps (except in special cases like along the equator or a meridian). Therefore, a line of constant bearing on Earth appears as a straight line on a standard Mercator map.