This article focuses on the development of a measure for frontage permeability, which we argue is needed to complement existing metrics used to describe urban environments and assess, amongst others, social performativity. Built density and street network centrality are two characteristics often discussed in relation to urban vitality. However, high densities and high centrality do not always result in higher urban vitality, which can be partially explained by a typical densification model often used in Brazil and in some other Latin-American cities with high-rise residential buildings. To understand the relation between urban form and social performativity, the metrics for density and network centrality are thus not sufficient and we propose to add two other urban form properties: frontage permeability and plot size. The hypothesis is that the mentioned densification model combines higher density with larger plots and lower permeability. Many scholars have shown that higher density is often associated with increased urban vitality, but larger plots are said to have the opposite effect and in Latin American cities, it is observed that lower vitality is found where buildings have less permeable frontages. This research aims at studying the combined effect of density, permeability, and plot size on urban vitality or, more generally, social performativity. However, there is no well-developed method to measure frontage permeability. Therefore, this article first presents a method to measure frontage permeability, both in qualitative and quantitative terms. This measure is then combined with existing measures of density and plot size to analyse how these three urban form metrics relate to each other. In a forthcoming paper, pedestrian observation data will be added to the analysis, to be able to give more insight in the relation between the three urban form metrics and urban vitality using pedestrian counts as proxy. We will show that the developed measure seems to be coherent and effective in describing permeability. Further, the preliminary results confirm the hypothesis that the Brazilian densification model with high-rise residential buildings generates a decrease in frontage permeability, although it does not appear to significantly change plot sizes.
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