The “Third Landscape” and the Rural–Urban Spaces in the South of the Community of Madrid, in the Field of Sustainability: A Case Study

The present research aims to analyze, assess, and interpret the territorial reality of the south of the Community of Madrid, with the case study of Aranjuez, revealing the interrelationship between urban growth, its link with the mechanisms that operate in the real estate sector, the processes of transformation of rural areas into spaces where rurbanization and marginal urbanization related to the reclassification of land (generally rural) prevail, based on the application of a novel interpretive methodology of the so-called “Third Landscape”, based on the “Key Performance Indicators (KPIs)”, applied to formal, socioeconomic, functional, environmental paradigms, among others. Thus, throughout the study, we address the Third Landscape and elements such as Lost Spaces, Garbage Spaces, Shadow Places, etc., in short, vacant lots or residual spaces (formless and unused anti-spaces), which are framed around the conceptualization of the Third Landscape, of that of no man’s land, which no one uses, whose maintenance is unknown, and which currently predominates in the rural and rururban world of Aranjuez. With all this, the motivation for the research and, therefore, its results, is based on the knowledge of the regeneration and adaptation of the nature of the study area in marginal and unplanned spaces—such as roadside ditches, vacant lots, and urban interstices—promoting the foundations for future territorial development models, as well as territorial planning processes that allow for urban regeneration, ecological design, and the socioeconomic enhancement of a city in expansion and transformation.