@DLL I work in the imaging business and to me, that looks very much like a scan of an OS map with some modifications done by software to add the route of the march and point of interest along the way.
The source of the mapping doesn't look OS to me - the contours are weird, and have height colours, plus the colours and icons are wrong. I've seen that mapping type before - can't place it though. Presumably some small mapping company.
(For the benefit of the doubt, I am talking about the provider of the maps in the book
)