Are you getting tired of the praise heaped on you for this tool? If not let me add to the chorus! Your tool is actually most versatile, since a non-airline entity could just replace the from/to airport codes with their own place names (say for a trade route viz tool, or a population migration viz tool...)

Very curious abt which software you used to write your code in - (I did search and found you definitely do not want to share the source code, so I didn't go there) -

The reason I ask is, my potential use of the tool would be a little different - I am using tableausoftware to map some of our data which is travel-related, but NOT airline-specific, and I wanted to go in slightly different direction with your software, to see if a modified version of it could be added as a plug-in of sorts to my tableau files, or...??
So to modify it..while I could add a 'dummy" airline with my data to my copy of the airlines.dat and routes.dat files, unfortunately my routes would be multi-segment and not non-stop (like all yours seem to be.) So I would want to add (a maximum of) 16 destinations for every row in route.dat, and then the application would need to read that and plot accordingly.

Which is why the question on the software used by you..

Thanks for a great versatile tool.