What is a rhumb line?

• A. An arc crossing all meridians of longitude at the same angle
• B. A line of constant latitude
• C. A straight line along a meridian
• D. A line perpendicular to all meridians

Answer: (A)

A rhumb line is a path that maintains a constant bearing relative to true north, meaning it crosses all meridians of longitude at the same angle as you travel. That steady angle is what defines the line and makes navigation along it predictable—the compass heading stays the same all along the route. On a Mercator chart, rhumb lines show up as straight lines, which is why they’re convenient for plotting routes with a fixed compass direction. This differs from a great-circle route, where the bearing changes along the way and the path appears curved on Mercator maps. The idea that the line crosses every meridian at a constant angle is the defining feature.