Good jazz improvisation follows rules of economy; variations pick out an element to explore, otherwise they lose focus; the harmonic reversals are disciplined by what came before. Above all, the jazz musician has to select elements for his or her own instrument that someone playing a different instrument can respond to. A successful improvisation will avoid sounding like the equivalent of a visual maze.
So too for people who improvise street use. In the surviving street cultures of the Lower East Side, booksellers clump together but display wares that separate themselves from their neighbors, like a musical theme and variations; hawkers using the steps choreograph themselves s that browsers can move from stop to stoop; tenants hang out laundry from house to house so that key windows are not blocked. To the casual visitor it may look like a mess, but in fact the street dweller has improvised a coherent, economical form. Rudofsky (Architecture Without Architects) thought that this hidden order is how most settlements of poor people develop and that the work of improvising street order attaches people to their communities, whereas ‘renewal’ projects, which may provide a cleaner street, pretty houses, and large shops, give the inhabitants no way to mark their presence on the space.