The form based codes, which are a matter of interest in the United States and are related to the New Urbanism movement, are to a large extent a recuperation of the way the old architecture bylaws were defined in many cities before the massive arrival of the car. There is even a Form Based Codes Institute which studies the issue.
Among the issues that this trend raises is the idea of urban aesthetics, and, more specifically, the relevance for urban planning of architecture, and, more specifically, that of a certain idea of uniformity in that architecture coming from the regulation. This uniformity is not, however, just the result of an aesthetic quest, but part of a wider sustainable development strategy, in which order is just an instrument. And uniformity concerns defined areas, not whole cities.
The Chicago Metropolitan Agency for Planning has published a book for communities on the issue. The project is oriented towards neighborhoods or similar scopes, not necessarily entire municipalities, and it must have an important public participation process. The final tool is organized as a zoning bylaw, as this is the USA; it is worth reminding, for non- US based readers, that the US zoning is not exactly the same thing that urban planning is in other countries, especially in Europe, where planning must integrate, as mandated by national law, what in the US would be Planning.