Which projection is widely used for sea navigation because it preserves direction and has straight rhumb lines?

• A. Gall Projection
• B. Miller Projection
• C. Cassini Projection
• D. Mercator Projection

Answer: (D)

The key idea is that navigators rely on maps where a constant compass bearing becomes a straight line. The Mercator projection does exactly that: it preserves angles locally (it’s conformal), so a line representing a constant bearing—a rhumb line—remains straight on the chart. This makes plotting a ship’s course straightforward, since a navigator can draw a single straight line to follow a chosen direction over long distances. While it distorts distances and areas—especially toward the poles—the ability to maintain a constant direction along a straight line is what makes it the go-to chart for sea navigation. Other projections may preserve area or reduce distortion in other ways, but they do not keep rhumb lines as straight lines, which is why they’re not favored for plotting navigational courses.