Earlier this week, my colleague Jason Krupp discussed the consequences of overzealous urban planning. Drawing from a recent paper by urbanist Alain Bertaud, the premise is that too much planning control impedes the efficient functioning of cities, producing unintended and undesirable outcomes.

One commenter on the piece noted that this perspective was all a bit “too free-market”, and that “good planning has a vital role in getting regulatory settings right”.

Certainly, good regulatory settings matter for effective planning. Urban planning, which serves to delineate the boundaries between public and private space is essential. Urban design, where planners artificially determine what private activities can take place and where, is not.

Economist Paul Romer made this point recently. Establishing the share of public and private space is the only thing that needs to be planned up front for undeveloped land. “A quality city needs a substantial amount of public space if it is eventually to support high density.”

Romer points to mid-town Manhattan as an example of a city that illustrates exemplary urban planning. Today, roads and sidewalks alone account for almost 30% of the surface area of Manhattan. The generous allocation of public space drawn into the 1811 plan, when New York City was mostly rural farmland, has allowed the city sufficient flexibility to grow into the cultural, financial, and social hub it is today.

Fail to allocate adequate public space however, and a city is shackled by the extent to which it can efficiently expand. Extending the network of public amenities to cater for growth then requires the costly demolition of existing infrastructure or more expensive options. Which is precisely the problem Auckland City is currently facing, and why the City Rail Link, projected to cost a cool $2 billion, is proving so contentious.

Overzealous urban design on a citywide or macro scale can make the provision of critical public infrastructure much harder in the same way that a lack of public space can.

Urban design often demands too precise a conception of a city, especially when it comes to public spaces. Few understood this better than urbanist Jane Jacobs: “The more the planner tries to predetermine the kind of activities the people who use it can do in it, the less likely that her design will complement the spontaneous contact that generates and diffuses new ideas.”