The study of crystal structures has had an ever increasing impact on many fields of science such as physics, chemistry, biology, materials science, medicine, pharmacy, metallurgy, mineralogy and geology. Particularly, with the advent of direct methods of structure determination, the data on crystal structures are accumulating at an unbelievable pace and it becomes more and more difficult to oversee this wealth of data. A crude rationalization of the structures of organic compounds and the atom coordinations can be made with the well-known Kekule model, however, no such generally applicable...