Restricting the discussion of a major city to its actual municipal territory proves to be a difficult exercise when one considers that the dynamics of a metropolis todya is generated not by one but by several municipalities and also by counties. San Francisco -which has the status of both city and county- can however be distinguished from other American metropolises (excluding New York) because it continues to serve and the centre and focal point of the entire metropolitan territory known as the San Francisco Bay Area. This remains to case despite the fact that the city's demographics are small than those of San Jose, the flagship of Silicon Valley. We will argue that this situation is due to the city's urban density and to the quality of its urban public space (UPS), as the determining variable. UPS are part of its urban morphology, but also have been created by the resistance to certain of the municipality's development plans by San Francisco 'urban pioneers", a group which is notably composed of non-conformist communities.