Geographic data are modelled, analysed and used for decisions. These data are very often associated to imperfections (inaccuracy, incompleteness, ambiguity, etc.). This book will present the sources and the nature of geographical imperfections and methods to manage them. The theory will be presented and illustrated on examples. The book is intended for engineers, students, scientists who work with geographic data. The target readers consist of a broad community around geographic data, computer science, agronomy, geography, urban planning, and ecology, etc.