A lot of the time, I'm looking for a way to calculate the air-line distance between two places, most often city centers.
For example when I flew from Zurich to Helsinki I wanted to know how far it was. With Google Maps I can do it but not for the air-line distance.
So does anyone know a tool for doing this or can give me advice on how to do it manually using the geo coordinates? Then I could write my own little tool.