The territorial structure is such that it is necessary to go through a step of diagnosis. Ageing must be apprehended in all its aspects, but the multiplicity of actors involved prevents the local powers from getting a comprehensive vision of the stakes and from implementing the adequate policies. The gerontopôle of "Pays de Loire" has developed an original method of diagnosis consisting in a comprehensive approach so called DATEL (diagnosis for territorial action environment and longevity). It is based on three aspects: an analysis of the geographical areas, a diagnosis shared by citizens and local councilors according to the Vancouver method, and a prospective review of the medico-social and health situation which integrates all services and forces at work and their potential demographic evolution. This DATEL aims to give local politicians the means to take well-informed decisions that will sustain the rapid demographic evolution of the ageing population and will maintain a good quality of life for our elders.