Measuring chart distance
Distance on a chart is the length you measure along the track line times the chart scale, converted to nautical miles.
- Read the scale off the chart: a VNC is 1:500 000 (TC AIM MAP 2.5.1), a VTA is 1:250 000 (TC AIM MAP 2.5.2), twice the detail and half the ground per cm.
- On a VNC, 1 cm = 500 000 cm = 5 km ≈ 2.7 nm.
- A nautical mile equals one minute of latitude (TP 1102), so you can read distance straight off the latitude scale up the side of the chart.
- Keep units straight:
1 nm = 1.852 km, and a nautical mile is longer than a statute mile.
Trap: leaving distance in kilometres or statute miles instead of nautical miles, or reading the wrong chart's scale.
References
- TC AIM MAP 2.5.1 (VNC 1:500 000 scale)
- TC AIM MAP 2.5.2 (VTA 1:250 000 scale)
- TP 1102 (one minute of latitude = 1 NM)
- AC 100-001 glossary (nm = 1.852 km, nm = 1.152 SM conversions)