The paper reflects on how ESDP (European Spatial Development Perspective) principles can be applied in territories with weak population patterns in quantitative terms. The ESDP defines a functional urban area (FUA) as the influence area of a city and sets a minimum threshold of 15,000 inhabitants for the city and 40,000 for the entire FUA. These thresholds are taken as guidelines to explore the concept of functional regions, adding more information from several sources. Hence the paper starts under the normative background given by EU spatial policy and proposes a methodology of analysis combining several techniques, including an application for the Castilla–La Mancha autonomous region (ES42 in NUTS 2). The approaches used in the method proposed include data from mobility, commuting, accessibility and qualitative analyses of services. The outcome shows how ESDP principles could be applied in practice in places with low-density settlement.