Most-served flight routes

What "most-served" means here

For each unique source-to-destination airport pair, the routes table is grouped and counted by the number of distinct airline codes filed against it. Pairs at the top of the list are the markets most contested by competing carriers, usually dense intra-European, trans-Asian, and US domestic shuttle pairs that throw off enough revenue to support multiple operators. Pairs further down can still carry heavy traffic, but they're usually dominated by a single national or regional carrier rather than carved up between several.

Use a route's page to see both endpoints together, the airlines on file for the route, and short notes on the great-circle distance and direction.