Book excerpt: Knowledge about distances---along with knowledge about spatial direction---is one of the most important fundamentals for a cognitive agent's orientation, navigation, and route planning. However, only some distances can be perceived directly. Therefore, knowledge about distances must often be inferred from other sources of information. In cognitive science research on spatial cognition, this is investigated in different ways, using empirical studies, computer simulations, and knowledge representation approaches. This book presents a comprehensive interdisciplinary study of human distance cognition. It discusses results on knowledge about distances from artificial intelligence research and cognitive psychology, proposing an integrating formal framework. Focusing on knowledge about route distances, it then presents a computational model of the way in which humans infer knowledge about distances in environmental spaces like cities or buildings.