Cardiff or Seattle?

The busiest departure cities for these two, with a place kept for each other part of the world. Busiest means arriving passengers where an official count exists, and where none does, the number of non-stop services flown: official route statistics are published by the European reporting countries and by nobody else, so a table ranked on them alone would offer a reader in New York or Tokyo ten European cities. Flying times are estimated from the distance between airports, and every row is a city flown non-stop to both. Where the typical offer connects anyway, the stops are shown. Under each figure is the airport the flight lands at and how far that is from the centre, because the nearest airport is not always the one a route is flown to. Where both columns name the same airport it is one flight, and the difference between the two is the distance printed beside it. Typical return fares for 2026-09 to 2026-10, cached market data up to 7 days old. The figure is the middle half of the offers found, so a single price means they agreed and a range means they did not; for a typical route that middle half spans about a quarter of the median, and for the least settled routes rather more than the median itself.