My highschool geography teacher once told me that if you take a flight from Amsterdam to New York, you sort of fly over Iceland due to the curvature of the earth. Looking at my textbook map, this idea seemed kind of ridiculous because a straight line doesn't bring you anywhere near Iceland. You'd need curved maps or 3D maps. I don't think I outright believed him, but I have been on enough flights since to know that this effect does affect a plane's trajectory. I just still don't have an exact idea how much.
Now it seems I have a problem along a similar vein. I did a long distance data collection contract and noticed I was constantly adjusting my course because I kept tracking the indicator on the navball for the first objective. I started out at 207° and near my destination it had shifted to something like 250°. I had been flying in a giant curve because I had assumed the indicator would adjust for the curvature of Kerbin.
Ideally I only would have had to point my plane into a direction once to reach my final destination. It seems I have to guestimate instead. How do I aim for the actual shortest route to a location that's nearly on the other side of Kerbin? I assume someone made a mod for this already, but I'd like to know if there are any tricks to get pretty close to it.