In my first paper to this Symposium, it was argued that the human cognitive subjectplayed a key part the shaping and working of the city. The key mechanism was thesynchronisation of diachronically experienced (and usually diachronically created)information into higher order pictures of spatial relations, the guiding form for whichwas an abstracted notion of a grid formed by linearised spaces. This notion wasargued to be both perceptual and conceptual, serving at once as an abstractedrepresentation of the space of the city and as a means of solving problems, such asnavigational problems. In this paper, the question addressed is where the notion ofthe ideal grid comes from, why it has the properties it does, and what it has to dowith the real grids of cities, which are commonly of the 'deformed' or 'interrupted'rather than 'ideal' kinds (Hillier, 1996). The answer, it is proposed, lies in the verynature of complex spaces, defining these as spaces in which objects are placed so asto partially block seeing and going, and, in particular, in certain divergences in thelogics of metric and visual accessibility in such spaces. The real grid, deformed orinterrupted, is, it is argued the practical resolution of these divergent logics, and theideal grid its abstract resolution. In both resolutions, however, the resolution is moreon the terms of the visual than the metric, suggesting that cognitive factors are morepowerful than metric factors in shaping the space of the city. The question is thanraised: do people have or acquire the concept of the grid, perhaps as some kind ofperceptual-conceptual invariance of spatial experience in complex spaces, and dothey use it as a model to interact with complex spatial patterns of the urban kind?This possibility is examined against the background of current opinion in the cognitivesciences
