The space we see around us is the end product of a long series of processes: physical, physiological, and cognitive. It is a highly structured perceptual entity. In contrast to the fact that most studies of visual perception are concerned with local phenomena in this visual space, the main purpose of this book is to discuss the global structure of visual space. The physical space which surrounds us is of Euclidean structure, but its perceived image is not necessarily structured in that way. Problems such as why the sky appears as a vault and why the horizon is located at eye level are discussed in the book.