🔍 Key Concepts

• Relationship between nautical miles and the geographic coordinate system (latitude and longitude) • How minutes and degrees are subdivided on the Earth’s surface • On a Mercator chart, which scale (latitude or longitude) is used to measure distance with dividers

💭 Think About

• Think about how many degrees and minutes of latitude span from the Equator to the pole, and how many nautical miles that represents. • Ask yourself: when you lay dividers on the chart to measure distance, do you step them off along the latitude scale or the longitude scale? Why? • Consider whether the spacing of meridians (lines of longitude) stays constant or changes as you move toward the poles, and how that affects using longitude to measure distance.

✅ Before You Answer

• Verify the definition of 1 nautical mile in terms of Earth’s geometry (degrees/minutes of latitude). • Check which axis on a Mercator chart (vertical for latitude or horizontal for longitude) gives a constant distance scale. • Confirm that distance on a Mercator chart is always taken from the latitude scale at the mid‑latitude of the track.