San Francisco has long been called the most European of American cities, a comment more often made than explained. What I think its speakers mean is that San Francisco, in its scale and its street life, keeps alive the idea of a city as a place of unmediated encounters, while most American cities are becoming more and more like enlarged suburbs, scrupulously controlled and segregated, designed for the noninteractions of motorists shuttling between private places rather than the interactions of pedestrians in public ones.