This is a quick tool for calculating the distance in km between two locations by inputting their latitude and longitude.
It also gives you the number of minutes it would take a sound to travel from one location to the other if there was no decay.
For example if someone clapped in Zurich, and it were somehow still audible in Athens, it would take ~80 minutes.
It uses the Haversine formula which treats the earth as a perfect sphere so there is very nominal margin of error.
Coll can read a text document featuring a list of cities and longitudes / latitudes.
Here is an example text file that you can load into coll:
AnnArbor, 42.291173 -83.716090;
Belfast, 54.587731 -5.935482;
London, 51.473629 -0.038005;
Zurich, 47.398033 8.550534;
Athens, 37.989842 23.732406;
Boston, 42.337368 -71.099299;
Portland, 45.511454 -122.645646;