Rundown neighborhoods as marginal systems
Another example of the importance of marginal systems concerns the sources of both cultural and enterprise innovation and their relationship to urban renewal. Jane Jacobs pointed out that one of the values of rundown urban neighborhoods was that they provided cheap rents in old warehouses, shops and houses, where small start-up businesses could establish themselves. She provided evidence that the elimination of these areas by urban renewal programs in the 1950s and 1960s was killing the economic life, as well as the artistic and cultural life, of American cities. There is tension between the "tidy up" mentality that wants to recyle and make full use of everything, and the mindset that values leaving things be to see what emerges. The balance is a fine one, whether we are working in the garden or planning a city.
-- David Holmgren, Permaculture: Principles and Pathways Beyond Sustainability