I read a lot of the GGG threads that are posted here but those about ancient dwellings and mounds interest me the most. These lines are interesting to me because of their scale. It would seem that mountainous terrain would pose a much greater difficulty than flat land. Those on flat land are the ones I'm vaguely familiar with.
Sometimes crop circles are done on terrain and you wonder how they do the layout. It has to involve more than scaled up drafting tools. The Nazca figures were done without being able to see them from above unless they had hot-air balloons, which is barely possible, but on flat land it could be done without much trouble even if nobody could see the results.