 His book "Collage City" (with Fred Koetter) is his theoretical treatise that sets out various analyses of urban form in a number of existing cities known to be aesthetically successful, examining their actually existing urban structure as found, revealing it to be the end product of a ceaseless process of fragmentation, the collision/superimposition/contamination of many diverse ideas imposed on it by successive generations, each with its own idea.In architecture his thinking paralleled his ideas about the city