grid theory ! pictures in links
Movement: the strong force
The ‘urban grid’, in the sense used in this paper, is the pattern of public space linking the buildings of a settlement, regardless of its degree of geometric regularity. The ‘structure’ of a grid is the pattern brought to light by expressing the grid as an axial map1 and analysing it configurationally. A series of recent papers have proposed a strong role for urban grids in creating the living city. The argument centres around the relation between the urban grid and movement. In ‘Natural movement’ (Hillier et al, 1993), it was shown that the structure of the urban grid has independent and systematic effects on movement patterns, which could be captured by ‘integration’ analysis of the axial map2. In ‘Cities as movement economies’ (Hillier, 1996b) it was shown that natural movement – and so ultimately the urban grid itself – impacted on land-use patterns by attracting movement-seeking uses such as retail to locations with high natural movement, and sending non-movement-seeking uses such as residence to low natural movement locations. The attracted uses then attracted more movement to the high movement locations, and this in turn attracted further uses, creating a spiral of multiplier effects and resulting in an urban pattern of dense mixed use areas set against a background of more homogeneous, mainly residential development. In ‘Centrality as a process’ (Hillier, 2000), it was then shown that these processes not only responded to well-defined configurational properties of the urban grid, but also initiated changes in it by adapting the ‘local grid conditions’ in the mixed movement areas in the direction of greater local intensification and ‘metric integration’ through smaller scale blocks and more trip-efficient, permeable structures.
Taken together, the three papers describe aspects of a generic mechanism through which human economic and social activity puts its imprint on the spatial form of the city. The papers do not deal with the patterns of activity themselves, but the theory seems to work because, regardless of the nature of activities, their relation to and impact on the urban grid is largely through the way they impact on and are impacted on by movement. Movement emerges as the ‘strong force’ that holds the whole urban system together, with the fundamental pattern of movement generated by the urban grid itself. The urban grid therefore emerges as a core urban element which, in spite of its static nature, strongly influences the long-term dynamics of the whole urban system. In the light of these results, we can reconceptualise the urban grid as a system of configurational inequalities– that is, the differences in integration values in the lines that make up the axial map – which generates a system of attractional inequalities– that is, the different loadings of the lines with built form densities and land-use mixes – and note that, in the last analysis, configuration generates attraction.
