Discovery Sheet No. 21 covers County Down.
Discovery maps are produced at a scale of 1:50,000 (or 2cm on paper equals 1 kilometre on the ground). Each Discovery Sheet covers an area of 40km x 30km surface area (with the exception of several portrait-format sheets, which are 42km x 32km). This is a comprehensive series of feature-rich maps which show detailed landscape information, like rivers, lakes, contours and many townland names. The Discovery Series is designed primarily for tourist and leisure activities; these maps are the preferred choice for hill walkers and those in pursuit of the great outdoors. It is also an ideal reference for location-focussed business use, in pocket-friendly folded form or as a wall-mounted reference.