"useless in practice , unless you ignore the bogs , rivers , lochs and contours"

I don't know, it IS useful to have some prominently visible features at both your origin and destination, they give you a nice sense of the straight line between the two and then you make pragmatic diversions as and when you encounter bogs and rivers etc. I used to navigate in London that way, trying to keep the sun at a particular angle to my car for as much of the journey as possible. It works well and you can choose dozens of routes and go for miles and still get there or thereabouts efficiently. So I think Alfred was probably onto something but I agree, you could never demonstrate it on a map only on the ground - by seeing whether the points were prominently visible. So the 2 cases are rather similar.