High Density Development
It was the opinion of "orthodox" urban planners that high density in cities was responsible for many undesirable effects like crime and filth. Jane Jacobs used her intuition and ground-level observation to see that not only was this not the case, but that high density cities could even be positive. Without advocating for overpopulation, Jacobs argued that a critical mass of people was necesary for the vitality of urban areas. Reaching this mass ensured many important side effects like increased economic activity, more people on the streets (which in turn leads to more safety), and a general sense of liveliness that corresponds to higher productivity and positive outlooks.