Megapolisomancy is a fictional occult science created by Fritz Leiber, an influential American writer of fantasy and science fiction. Featured in Leiber's novella Our Lady of Darkness, megapolisomancy is the art of predicting and manipulating the future through the existence of large cities.
Derived from the English megalopolis and Greek manteia ('prophecy')
In Our Lady of Darkness, the primary practitioner of this pseudoscience is fictional occultist Thibaut de Castries, whose seminal work, Megapolisomancy: A New Science of Cities, concerns the physical, psychological and paramental (spiritual) effects of certain substances, including steel, electricity, paper, and so forth as they accumulate in cities. This book was primarily a book of occult theory; De Castries preserved all of his actual methods for practicing megapolisomancy in a second book, which he referred to as his Grand Cipher or Fifty-Book. The latter book contained a series of 50 astrological and astronomical signs and other cryptic sigils.