I found that the simplest way to complete all challenges was to watch video guides on YouTube. I followed the video guides on YouTube channel "GamingsinceGaming" and these are highly recommended. In each location the guy in the video clearly shows you where you need to be by showing you the location on the map and then zooming in before then leading you to the exact spot whilst he talks you through it. Excellent guides and I would have struggled with this achievement if it were not for them.
https://m.youtube.com/playlist?list=PLWtd0ISBZPcM1e0E89cUBjA...