So, they e scanned aerial images?
Yes, but that’s not all, Once in digital form, the images undergo a computer orthorectification routine, making them geometrically like maps. This means a number of things, including the fact that, when you look at an orthorectified image, no matter where you look, you’re looking straight down–just like looking at a map. Rather more importantly, it means that it is possible to make accurate measurements of ground distance on the photos, as one can on maps, and that the photos can be used in automated mapping software along with other digital cartographic data.
