Turning a map angle into distance
A degree of latitude is divided into 60 minutes, just as an hour is divided into 60 minutes. Because lines of latitude run around the globe, a minute of latitude represents a small north–south step along a meridian—the line running from pole to pole.
The Earth’s circumference is about 40,000 kilometers. Divide a full north–south circuit into 360 degrees and then 60 minutes per degree, and each minute comes out close to 1.85 kilometers: one nautical mile.
Why the match is useful at sea
On a nautical chart, a navigator can measure a route with dividers and compare that span with the chart’s latitude scale. Since one minute of latitude is approximately one nautical mile, the map’s angular markings also serve as a practical distance ruler. The scale is taken from latitude, not longitude: meridians draw closer together toward the poles, so a minute of longitude does not represent the same distance everywhere.
The relationship is an approximation, not a perfect property of the planet. Earth is slightly flattened at the poles, which makes the distance covered by a minute of latitude vary a little from place to place. To give navigation a consistent unit, the nautical mile is standardized at 1,852 meters. Its close connection to latitude remains a handy bridge between a position measured in angles and a journey measured in distance.
