Twisst-follower @rolandtaams just asked a question I didn't really know the answer to: if ISS travels from West to East over my head, how far does it actually travel?
From looking at the maps in GoSatWatch, I know that when ISS comes up here in the Netherlands, ISS is still above the Atlantic ocean. When it passes high and can be seen all the way to the horizon in the East, it's already above Russia. So that would be about 3.200 kilometers or 2,000 miles.
Let's assume it is visible all the while it passes you, and it travels at 400 kilometers at 7,7 kilometers a second. It would be relatively easy to calculate the distance in space, but how much is that on the ground?
Personally I'm terrible at math, but if you have a suggestion for a method, please tell everyone in the comments below!