General Pocket Planes knowledge with calculation results for distances between airports in particular.
City data I believe was originally obtained at https://therustysnowman.com/proj/pocketplanes.php No longer up, but same information now appears to be hosted at https://jayisgames.com/walkthroughs/pocket-planes/pocket_planes_tools.html I also derived city data for the 5 new cities in the 2.17 update using PP_wrap_pub.py
Pre 2.17, the two cities furthest apart were Nome and Wellington (2785 coins/12 bux) The two class 3 cities furthest apart were Los Angeles and Tokyo (1991 coins/9 bux)
As of 2.17, the two cities furthest apart are Tiksi and Punta Arenas (1872 coins/8 bux) The two class 3 cities furthest apart are Seoul and Buenos Aires (1552 coins/7 bux)