For anyone who needs a polyline for Hadrian's Wall, here it is! Please use this link. I'm planning on refining it in the near future, which shouldn't take too long. As I wasn't able to access more refined information on the wall some of this is educated guesswork based on an OS 1:25,000 map and some Satellite imagery, as well as some other sources. Any students/practitioners of any subject that involves Hadrian's Wall are free to use it, although I would like you to reference where you got it from (i.e. this blog!!) and the problems with the dataset (not accurately referenced, should be used as a rough guide to the location of the wall etc.). It has a few attributes that can be filled in, depending on whether it is Hadrian's or Severan's Wall.