Early on in Terry Pratchett's novel The Light Fantastic, a spell is cast to map the world. It begins as a "fireball of occult potentiality," dangling in the Great Hall of the Unseen University, which evolves into a ghostly "embryo universe." The embryo expands "lightly as a thought," with spectral continents "sleeting" through walls and people. It surges across the landscape until the entire population and geography of the Disc is exactly duplicated and enclosed by a shimmering shadow-self of "shining threads that followed every movement."
