This article aims to understand the probable links between social capital and social infrastructure. The inclusion of these two dimensions into urban analysis may help to better understand the nature and characteristics of the relationships between the built environment and the level of organisation of the residents, and whether these have an impact on the vulnerability of the territories. Through use of statistical techniques (visual grouping and cluster analysis, among others), this article seeks to construct a comprehensive measure of social capital, as well as a comprehensive index of social infrastructure. These two in combination show, as the main results, that the characteristics of the built environment may promote higher levels of social interaction, also leading to higher levels of civic engagement and participation. However, the results also suggest that this relationship may be bidirectional. Finally, the mapping of the two indices applied in the city of Barcelona is presented and these results are compared with a previously constructed index of vulnerability for the same territory, allowing an overall better understanding of Barcelona’s socio-urban behaviour.