Why not just buy the map? It covers an area far bigger than you can cover in a day so it will give you many many rides, it doesn’t need batteries and it shows you all the attractions close to your chosen route, unlike viewing the map on a small screen, which is like reading down a rolled-up cardboard tube.
Not to mention that OS maps, being folded, make excellent on-the-bog studying material – many’s the time I have staggered out of the bathroom with my legs numb from sitting for half an hour or longer, absorbed in the study of new routes.