The second volume of Ildefons Cerdà’s Teoría General de la Urbanización —a work that defines urban planning as a science for the first time— includes an extensive set of statistics and property registers of Barcelona that served as a basis for the design of the city extension plan and made it possible to establish relationships between urban conditions and their impact on mortality and to argue and justify the need to expropriate a generous amount of land to make new roads. Years later, under the motto ‘survey before planning,’ Patrick Geddes introduced in Cities in Evolution the need for observation and profound knowledge of the city and the territory prior to any urban planning action. This view accepting urban planning as scientific knowledge was conditioned by the method. Later, in 1970, Manuel de Solà-Morales emphasised in La ciudad y los juegos that ‘urban planning, as a social science, suffers from the difficulties of working with an ambiguously defined body with minimal testing capacity’. The aim of this statement was to establish the need to build abstract city models based on logical and mathematical formulations that would act as laboratories of reality where acting principles would be validated and not just the result of ideological apriorisms. Although this line of work was clearly identified by Solà-Morales, he did not continue it; instead he focused his activity on the knowledge of city
morphology.