Zoning is a form of “indirect” urban design, as its rules and restrictions dictate what can be built on each parcel in most American cities. Though designers rarely write code themselves, zoning affects the urban form in many ways. Every road width and building height delivers a message to their users on how to use the public realm. In fact, zoning code is often written by engineers or lawyers as opposed to planners and designers. Zoning typically regulates land use as well as basic building dimension and design details.


Zoning codes have evolved over the years as urban planning theory and political priorities have changed. Many old zoning codes, like Philadelphia’s, are outdated and economically inefficient, and do not have the flexibility in their parcel-by-parcel designation to allow for smooth transitions to new land uses.


An entire rezoning is time-intensive and strictly adhering to outdated code can hinder development. Therefore, many cities loosen their amendment process to help landowners change the zoning code quickly, or simply ignore the code and let developers build structures that directly violate the ordinance. This explains the negative connotation surrounding the Philadelphia zoning code, which is so old that it is seen by many as a direct hindrance to progressive development that could help make the city a more world-class destination. Many developers see zoning here as an obstacle to overcome, not as standards that must be met to integrate into the surrounding community.


Many cities are experimenting with different zoning types. Some more flexible zoning forms include (1) form-based zoning, which regulates by design instead of use; (2) incentive zoning, which rewards developers for meeting certain urban design standards, and (3) performance zoning, which allows landowners to meet building goals by achieving various levels of compliance. Philadelphia Mayor Michael Nutter created the Zoning Code Commission to begin a re-zoning process for the city. The ZCC hired two primary consultants, Clarion Associates and Duncan Associates, who submitted their recommended changes to the code language to the ZCC in September 2009.


Zoning is not used in all American cities. Houston is the largest U.S. metropolis without a zoning code in place, as citizens continue to reject efforts to implement it.