This web site shows flight routes from world's 50 busiest airports by passenger traffic, according to Airports Council International data from year 2014.
You can see how an airport is connected with the rest of the world.
For more info visit Geographica at GitHub
Data sources
Passengers data: Airports Council International
Airports data: http://ourairports.com
Routes data: http://openflights.org
Disclaimer: This data is not suitable for navigation.