Great Circle Mapper

     

     
     A great circle path is the shortest path on the surface of a sphere between two points on that sphere. Technically, the term geodesic path should be used since Earth is not a true sphere, but the great circle terminology is common usage. 
     The Great Circle Mapper website enables you to display maps depicting the great circle path between locations and to compute route distances. The maps can also show the area which is within a specified range of a location. The Great Circle Mapper includes an extensive database of airports and other locations with a search engine for searching this database in various ways and provides detailed information about locations in the database.
     To use the map to show a route you will first have to search for the airport's three letter designation. For example, New York's John F. Kennedy is JFK and Melbourne, Australia's Tullamarine Internationl is MEL. 
     Once you have obtained this information go back to the Home location and click on Map under Action where it says Map Paths and enter JFK-MEL and you will see the route and distance, in this case 10,374 miles. 
     The maps generated could be used in conjunction with the Flight Aware site I posted about HERE. 

Further reading about great circle routes can be found at the Smithsonian website.