The chart: position and distance
Distance between two latitudes
How to think it through
- 1You have two points on the same meridian; you want the distance.
- 2On the chart one minute of latitude is one mile: the distance is the difference in latitude.
- 3Always measure on the side scale, never on the top one.
Worked example
Every step says why you do it, which formula you use, the working and the answer.
Distance between two points on the same meridian
Points A and B lie on the same meridian. A is at 49°57.0′N, B at 49°44.5′N. How far apart are they?
- Point A
- 49°57.0′N 002°42.0′W
- Point B
- 49°44.5′N 002°42.0′W
How many minutes of latitude apart are A and B?
Why: On the same meridian the distance depends only on the difference of latitude.
Working: 49°57.0′N − 49°44.5′N = 12.5′
Answer: 12.5 ′
How many nautical miles is it from A to B?
Why: One minute of latitude is, by definition, one nautical mile.
Working: 12.5′ of latitude = 12.5 NM
Answer: 12.5 NM