Assessing Cities, A New System of Spatial Indicators

Salat, S., Bourdic, L., Nowacki, N.

Proceedings of the World Sustainable Building Conference SB11 Helsinki, Finland.

Urban form and spatial distribution of elements is a crucial factor for urban sustainability. Based on complexity theory of urban form (Batty, Hillier, Salingaros) the paper will propose new mathematical formulas for spatial and morphological sustainability indicators: intensity, diversity, proximity, complexity, form, connectivity and distribution. Intensity measures the density or concentration of an object on a given scale. It implies a relationship of efficiency between the result and the means employed. This is the case for the carbon and emissions intensity for example. Indicators of spatial distribution give the relative concentration or dispersion of objects on a given scale compared to the totality of known objects on a bigger scale. The point is to quantify the distribution of objects in order to evaluate the equitability. Proximity corresponds to the distance between two things, for example between homes and leisure activities or between offices and public transit stations. This distance must be minimized to minimize travel needs for day-to-day activities. Connectivity corresponds to the relative accessibility or spatial interconnection of a system or a network and will be assessed by the graphs theory and by fractal geometry. Diversity refers to the mix and variety of objects of a similar type on a given scale, for example, the diversity of land use or of housing size on the scale of a district. Unlike spatial distribution, diversity focuses on the frequency and scale of different objects not on their more or less homogenous location in space. The concept will be approached through scaling inverse power laws. Indicators of form refer through shape factors to the geometry of elements, their volume and their footprint in space. They measure this information as a basis for building formulas predicting energy consumption. These indicators allow comparing urban projects by verifying the energy, social and environmental consequences of choices of forms. Authors eventually present a table summarizing all the spatial indicators that can be used to assess urban efficiency