Walking and navigating For a really detailed map of the area, I'd recommend getting an Ordnance Survey Explorer Map. The Rule valley spans two of their paper maps, so I'd suggest getting a Custom Made Map, available online click here for more info. Selecting a 'Centre Point' location, Hallrule is a good centre point, you can choose your own text and image for the cover, giving it a nice personal touch.
Ordnance Survey also offer maps to view online. Perfect for planning walking holidays as the maps show rights of way, landscape features and places of interest (which is more detail than you get from a standard Google map).
Historical You can view historic maps of the area online at the Canmore website, click here. It took me a while to figure out but its worth persevering with. On the list of options, select "Zoom To" search for a place name eg Bedrule, click "Go". Choose "Historic Maps" from the right-hand menu, and there's a line of little square boxes that appear next to the list of old maps, click one, a tick will appear and it will bring the old map onto the main screen. You can then use the 'slider' next to the tick boxes to superimpose the old maps over newer ones to get a better idea of locations.
You can also search old photos and images on the Canmore site, which is a great resource.