Flight distances are not straight lines on a flat map—they follow great circle routes over Earth's curved surface. Understanding this helps interpret distance data and plan efficient routes.
What is Great Circle Distance
A great circle is the largest circle that can be drawn on a sphere, passing through any two points. The great circle distance is the shortest path between two points on Earth's surface. This is why flights from New York to Tokyo fly over Alaska—it's actually shorter than heading straight west.
The Haversine Formula
The Haversine formula calculates great circle distance from latitude/longitude coordinates. It accounts for Earth's spherical shape. More precise calculations use the Vincenty formula, which accounts for Earth being an oblate spheroid (slightly flattened at poles).
Nautical vs Statute Miles
Aviation uses nautical miles (1 nm = 1.852 km). Statute miles are the familiar land miles (1 mi = 1.609 km). Nautical miles relate to navigation: 1 nautical mile equals 1 minute of latitude. Always clarify which unit when working with distance data.
Real vs Great Circle Distance
Actual flight paths deviate from great circles due to wind patterns, restricted airspace, and air traffic routing. Westbound transatlantic flights are longer than eastbound due to jet stream. Great circle distance is theoretical minimum; actual flight distance is typically 5-10% longer.