Distance is a central element in the understanding and for the action on cities, on territories and on transport. However, distance has not been considered at its full potential in the disciplines that care about spatiality, namely geography, economy, psychology and sociology, and that constitute the main corpus used by the specialists of urbanism, spatial planning and transport.The investigation exposed in this memoir shows that the geographical interpretation of the mathematical properties of distances, and in particular the triangle inequality, reveals some key elements that allow for the establishment of a theoretical framework with direct interpretations for action on transport and on the territorial and urban arrangements.Hence, and contrary to many analysis found in the scientific literature partially linked to the influence of the euclidean paradigm, it is possible to state that distances are always optimal, that the detour is a contribution to this optimality, and that the pause in the movement participates in the establishment of the optimality of distances. The euclidean straight line is deeply rooted into the representations of actors that they be researchers, decision makers or users of urban spaces. The straight line is a reference for any movement; and yet the detour is so universal, extending to the extreme form of the spatial inversion, the pause is so frequent that they both should be treated in a positive way in urbanism and spatial planning. From this development, we set up an analytical framework based on two distances – the distance of density and the distance of transport – expressed under two different forms, euclidean distance and network distance. This framework permits to revisit a set of approaches, models and concrete solutions concerning cities, territories and transport: the conception of public spaces and urban form favouring walking, the organisation of railway stations and of their links with surrounding urban space, the treatment of sub-optimal situations generated by public transport maps designed for users, the fact of considering some external equipments as direct contributors to the openness of a territory, are examples of situations where the analytical framework can help to guide the action.Expressing and beefing up this reflection on distance, my research activity is then exposed according to three axis of researches. Firstly the distances of the shrivelled space represent a reflection started during the PhD on the deformation of space by the fast transport means. A second axis focuses on the distances between cities, and links the performance of transport systems with urban and territorial strategies through the development of indicators based on accessibility and the contact potential. The third axis concerns distances in the city with a focus on the urbanism of public transport, as a French version of the Transit Oriented Development (TOD).