FAQ
Flight Route Map FAQ: Great Circles, Flight Distance and Airport Codes
These questions cover common topics from spherical geometry to airport data, including what the tool can and cannot represent.
01
Why do aircraft not always fly a straight line on a map?
A map is a flat projection of the curved Earth. The geometric reference is often a great-circle route, while actual operations also respond to airways, winds, airspace and airport procedures.
02
What is a Great Circle route?
A Great Circle route is the shortest surface arc between two points on a sphere, lying on a circle whose plane passes through the Earth's centre.
03
Why does Mercator projection make routes look curved?
Mercator projection stretches scale toward high latitudes. A great-circle path can therefore appear as a northward or southward arc after the globe is flattened.
04
Why do flights to the United States pass near Greenland?
The spherical shortest path from Europe to North America can move into high latitudes. The curved map shape does not mean every flight uses the same waypoint.
05
Why do flights to Japan appear to pass near Alaska?
Spherical geometry makes some East Asia–North America routes bow north on a flat map. Winds and operational constraints still determine the actual track.
06
What is the difference between a Great Circle and a Rhumb Line?
A Great Circle is the shortest spherical path and normally changes heading. A Rhumb Line keeps a constant bearing and appears straight on a Mercator chart.
07
What does FlightRouteMap mean by flight distance?
It means the Great Circle Distance between airport coordinates, summed by segment. It is not the actual flown mileage of a specific flight.
08
How is the detour ratio calculated?
Detour ratio = (sum of adjacent great-circle segments ÷ direct origin-to-destination great-circle distance − 1) × 100%.
09
What is the difference between extra distance and detour ratio?
Extra distance is total segment distance minus direct distance in nautical miles or kilometres. Detour ratio expresses that difference as a percentage of direct distance.
10
What is ETOPS?
ETOPS means Extended Operations and concerns approval and planning conditions when applicable aircraft operate far from suitable diversion airports. This site's overlay is geographic illustration only.
11
What is an ICAO airport code?
An ICAO location indicator is usually a four-letter code used to identify locations in aviation operations and air-traffic systems.
12
What is an IATA airport code?
An IATA code is a three-letter airport or location identifier commonly used in passenger, airline, reservation and baggage systems, such as LHR, JFK and NRT.
13
Where do the airport coordinates come from?
The project ships a local airport dataset. Coordinates are validated during import and the same record is shared by the map, calculations and poster.
14
What information is in the airport database?
Records include IATA, ICAO, bilingual names, city, country, latitude, longitude, elevation, longest runway and a data-update field.
15
What is the airport data source?
The base dataset comes from OurAirports public data, with maintained Chinese names, aliases and overrides. The data page records the import date and limitations.
16
How often is airport data updated?
The dataset changes when the project imports a new release rather than through a live runtime query. Codes, coordinates and runway records can change between imports.
17
How many stopovers can I add?
The route editor currently supports up to 16 airports, which is enough to compare a route with many technical or commercial stops.
18
What happens if the origin and destination are the same?
Direct great-circle distance is zero, so the detour ratio is undefined. Adjacent segment totals can still be displayed.
19
How are routes across the date line handled?
The map splits paths at ±180° and uses a continuous world copy so a route does not draw a false line across the entire map.
20
How are near-polar routes displayed?
The globe uses a spherical view, while the flat map clips paths to the visible Web Mercator range. This explains geometry and does not represent an operational polar route.
21
Why can the result differ from Google Flights?
Google Flights reflects a date, flight, carrier and operational route. FlightRouteMap calculates a stable geometric baseline between airport coordinates.
22
Why can the result differ from FlightRadar24?
FlightRadar24 shows an observed or estimated track for one flight, including procedures, holding, weather avoidance and airspace constraints. This site is not a live-track tool.
23
Can weather change flight distance?
Yes. Thunderstorms, volcanic ash, icing and convection can require rerouting, while winds change the time- or fuel-efficient choice.
24
How do airspace restrictions affect a route?
Military areas, temporary restrictions, congestion and national route structures can all move an actual track away from the great-circle reference.
25
Are airport codes and city codes the same?
Not always. A city can have multiple airports, and some three-letter identifiers refer to a city or location. This tool uses the airport records in its dataset.
26
Why use nautical miles?
Nautical miles are common in aviation and marine contexts. The page also shows kilometres using 1 nautical mile = 1.852 kilometres.
27
How are distances calculated?
Each adjacent airport pair gets one great-circle distance. Total distance is their sum, while direct distance uses only the first and last airports.
28
Can I measure distance from the line on the map?
No. The line visualizes sampled spherical points; distance values come from an independent spherical calculation and are not derived from screen pixels.
29
What is the difference between the flat map and globe?
The flat map is useful for labels, the date line and route lists. The globe makes spherical arcs and high-latitude geometry easier to inspect.
30
Can I use this tool for navigation or flight planning?
No. Coordinates and airport information are for geographic display and distance calculation only, not navigation, flight planning, diversion decisions or operations.
31
Is my route uploaded to a server?
Route search and calculations run in the browser by default. Limited event data is sent only when the deployment explicitly configures an analytics endpoint.
32
Can I export a route poster?
Yes. The calculator can generate a route-map or detour-analysis poster with selectable ratio, units, codes, coordinates and map mode.
33
What if an airport record is inaccurate?
Treat the result as a geographic comparison and check the listed source data. Airport records can lag or contain errors and do not replace official aeronautical information.