The title comes from the poem And did those feet in ancient time by William Blake. It is now very well-known, in UK, as the anthem Jerusalem. ‘Green and pleasant land’ really refers to just England but the map includes the whole of UK and Ireland.
When you look straight at the map you see only stripes. As you move around the map appears and disappears.
The map in the photos was made using DK yarn but you can use any yarn and the illusion will still work. Using DK, the size is approximately 67 cm x 80 cm (26” x 32”). Using other yarns might change the overall size. I used about 400 metres (440 yards) in each of two colours. Extra yarn is needed for the border.