A useful guide for anyone thinking of walking in these two ranges.
Maps are large scale and give contours, rivers, lakes and paths, but are not as detailed as OS and would be best used as a useful addition not in place of.
The route up Tyfan and to Glyder Fach and Glyder Fawr is properly described and accurate with paths well marked. However, description is brief and because of this the challenge of this route is somewhat underestimated or underplayed.
The description of the Snowdon Horseshoe is slightly fuller, but by its concise nature fails to warn a novice how challenging the route is.
I'd suggest using this map as a very useful addition to the OS, but read more detailed descriptions of the routes before attempting them.