Human behavior can be both predictable and difficult to design for. Urban environments are unquestionably complex and dynamic in their design, yet are just as much a product of un-designed and leftover spaces of a continual evolving place. Designers intend to predict and assign appearances and usages to spaces yet through limited cultural expectations of the landscape design in urban settings, this is not the enduring result.
Freedom of expression on private property and allowing un-programmed activities in public spaces inherently prevents design from becoming static and controlled in character, however a better understanding of this loose programmatic design must be made. Graffiti may be a predictable activity in urban environments yet it has been experimentally but unsuccessfully designed for.
There is no one right answer to the question of design just as there is not always a clear line between personal expression, public art and vandalism. But by overlapping and redefining the design of complex spaces between different disciplines we might begin to better understand how to include activities such as graffiti, or prevent them without the expense of an overlapping use of the same space.