The 20th century saw significant transformations in the way cities and other settlements were planned and developed; these transformations were visible not only in architecture and urban form but also in the theoretical and conceptual models, modes of operation, and challenges these fields faced. At the same time, a remarkable consistency can be observed with respect to the sorts of environments envisaged in the sometimes radically different designs, which persist even today. Central to this consistency is arguably the persistence of forms of thinking that employ diagrammatic interventions in conceptualizing psychology, subjectivity, social life, architecture, and urbanity. This chapter intends to look at three particular aspects of the move by which diagrammatic inventions have been linked to conceptualization and to review the pervasive and continued impact that such thinking has had on architecture and urban design. Whilst these impacts are not always readily apparent, they cast light on why proposals for the “no-car society” often constitute carbon copies of solutions for the car society, despite posing as its antithesis.