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Non-residential economic activities are the heart of mixed use streets. That makes mixed use streets extremely difficult to plan and develop as the activities they support require certain conditions to flourish. Those conditions, in turn, depend on spatial as well as non-spatial drivers, and equally they depend on each other. Like the emergence and evolution of living organisms, that of mixed use streets goes through an infinite succession of individual and collective initiatives, the vast majority of which are destined to fail due to adverse environmental conditions. Managing such conditions is the only chance that designers have to influence the development and evolution of mixed streets in their plans. One of the most profound spatial determinants of non-residential uses in cities is street centrality. Multiple Centrality Assessment (MCA) is a computer-operated procedure for mapping the centrality of urban streets and spaces. It applies to spatial cases a set of methods drawn from research into the physics of complex networks in nature, society, culture and technology which emerged in the late 1950s and have gained momentum since the 1990s.