METHODOLOGY
How Flight Route Map calculates distance
Every figure uses great-circle distance on a sphere, then converts it to nautical miles and kilometres; map geometry and operational routes are separate concepts.
1. Adjacent segments
Each pair of neighbouring airports becomes one segment. MAN–DUB–IAD therefore calculates MAN to DUB and DUB to IAD.
2. Great Circle algorithm
The app uses airport latitude and longitude to calculate the shortest spherical arc, then uses matching spherical samples for the visual route. It never derives distance from screen pixels.
3. Total distance
Add every adjacent segment's great-circle distance to get the route total.
4. Direct distance
Calculate the great-circle distance from the first airport to the last airport, ignoring intermediate stops.
5. Detour ratio
Detour ratio = (total segment distance ÷ direct origin–destination distance − 1) × 100%. Extra distance = total segment distance − direct distance.
Units
Calculations use kilometres internally. Nautical miles use 1 nautical mile = 1.852 kilometres. Display values are normally rounded while calculations retain floating-point precision.
Map projection
The flat map handles Mercator display limits, the antimeridian and high-latitude clipping; the globe uses an orthographic view. Both modes share coordinates and great-circle samples, but a screen line is not a distance measurement.
Data updates and version history
Airport data is updated through the import script, which validates duplicate IATA codes, invalid coordinates and required fields. Source dates and limitations are recorded in data/README.md; content and calculation changes are retained in project versions.
Edge cases
When the origin and destination are the same, direct distance is zero and the detour ratio is undefined, while segment totals can still be shown.
Known limitations
The result does not include live flights, waypoints, weather, winds, air-traffic control, airport procedures or operational approvals, so it is not an actual flight track, navigation aid or flight plan.