For longitude, which scale on the chart should be used?

• A. Latitude scale
• B. Longitude scale
• C. Mercator scale
• D. Distance scale

Answer: (B)

Longitudes run north-south, so the chart provides a longitude scale along the top and bottom edges that labels degrees of longitude. To read or measure east–west position or the change in longitude between two points, you use that longitude scale because it directly corresponds to the longitude coordinates on the meridians. The latitude scale on the sides is for measuring north–south position, the distance scale converts chart distances to nautical miles, and the Mercator projection describes the map’s layout rather than providing a longitude-reading axis. Therefore, for longitude, use the longitude scale.