In the meantime, commenter Vince has written a critique of Portland's plans to regulate its burgeoning urban gardening movement which he develops into a thoughtful statement on the goals of planning and zoning itself:
"City planning and zoning departments have in mind exactly the sorts of things that ought to happen in exactly which places. They claim to be able to handle and mitigate the messy intricacies of highly complex cities and their inner workings. They seem to know precisely how many shopping centers we need, where they should be located, and how we should get there (exclusively by car.) They take measures to boldly separate people from where they work, dine and play so as to create economic dead zones (residential areas) across great swathes of our cities. The truth of the matter is that no one is able to accomplish the feat of city planning. Cities are a complex accumulation of unplanned human action, interaction and activity. To regulate that is to regulate human nature and civilization itself. At the city level, the best we can hope for is that some shot-gun style regulation doesn’t hit us in the rear end as planners try to make sweeping regulations that effect the lives of half a million people."For more critical writing on zoning and urban planning, try Bernard Siegan's 35 year old, but still relevant, article.