Planning theory is very different from urban theory. Urban theory tries to model how cities form, change, and grow.
Planning theory tries to model how cities are governed with future-oriented policies. Thus, one of the most important aspects of planning theory is to figure out what urban regimes actually are, and how they work. Obviously one piece of an urban regime is the formal government of a city. But as a local government, the municipality is usually subordinate to several higher levels of government, and they also play a role in the urban regime. The wealthy elite also play a governing role, both as ‘the business community’ and as the social network of charities, fundraisers, and influence-brokers. And on a more subtle note, an array of unwritten rules and expectations also govern urban space, from expectations of ‘proper’ behavior in public space to claims of specific, enforceable rights of property.
This is a much more fractional, distributed, de-centered concept of ‘urban regime.’ Rather than try to describe all the disparate elements that constitute an urban regime, a more concise approach is to ask a question: ‘This urban space is governed. Who and what governs it, and how?’ The answer to this question is not simple, but that is the point: we know what the urban space is; we see cities take form and transform. That does not mean that the entities and processes which govern urban space are as tangible and definite as the space itself. Since gasoline prices strongly influence land-rents in American cities, then OPEC governments all exert an indirect but strong governing power over American cities.
A very pragmatic branch of theory
Planning theory is related to theories of government, public administration, and decision-making within militaries, businesses, and nongovernmental organizations (NGOs, known in the U.S. as “non-profits”). Planning theory is distinctive because it focuses on urban environments and regimes; but given the extended nature of urbanization in the twenty-first century, perhaps the only way to delimit the scope of planning theory is scale: planning theorists do not focus on the internal decisionmaking processes of individual firms (the lower scale limit), nor do planning theorists focus too much on the desicionmaking of national regimes.
Furthermore, planning theory is a theory of practice, so the ostensible distinction between theoretical scholarship and professional practice is meaningless to planning theorists. Most of the time we are asking, ‘How was that decision made?’ ‘How did that policy succeed or fail?’ ‘How different were initial expectations from policy-outcomes?’
There is another, very negative connotation of ‘theory’ among Americans as ‘an ideal vision that cannot be implemented in reality’ (i.e., “in theory this should work”). This conception of theory is not very relevant to planners. Ideal visions of cities are sometimes studied by planning historians and architectural historians. But since they weren’t implemented, they don’t pertain to decision-analysis unless they influenced subsequent actual urban policies. For example, the Trylon and Perisphere of the 1939 New York World’s Fair are important to planning theorists because the associated Futurama exhibit influenced U.S. lending and taxation policies that promoted auto-centric suburbanization.