Half of the world's population now lives in cities. In Australia, this proportion is higher at over three quarters, spread across 17 cities, each with more than 100,000 people. The share of Gross Domestic Product (GDP) contributed by our cities (about 80%) is higher than the population share living in cities. Cities also are responsible for over three-quarters of carbon emissions. These relativities provide some insight into why cities are important. The concentration of people in cities increases both productivity and liveability, through scale economies and agglomeration effects in production and consumption.
Productivity, liveability and sustainability are critical goals for our cities. Managing the development of cities is fundamentally about finding the right balance between economic productivity, maintaining a high standard of liveability and achieving long term sustainability (social and environmental), as well as recognising that there are multiple interdependencies between these goal areas. Resolution of this balance will reflect local values and aspirations and will differ between cities and countries.
International research suggests that agglomeration effects in production typically range between 3% and 8%, meaning that doubling city size can be expected to lead to output increasing by 103-108%. Relative output increases in knowledge-intensive industries, many of which tend to concentrate in CBDs and other urban hubs (e.g. universities), are typically higher.
Agglomeration effects in consumption, an important element of liveability, are a relatively new area of quantitative research. Recent German analysis, for example, provides clear evidence that bigger cities (in population terms) show benefits for residents through a larger range of service choices, across areas like restaurants and bars, concerts, dancing, theatres and museums.
There is a trade-off in city size between agglomeration benefits and increasing external costs such as traffic congestion, crime, pollution and noise /sustainability concerns). Large cities that are compact and enjoygood accessibility, matched by efficient transport infrastructure, are among the most efficient urban settlements. These cities do not arise by chance but require decades of careful management and guidance. US urban scholar, Robert Cervero suggests that, beyond about 5-10 million, the increasing social costs of size exceed the additional benefits.
Australia's major cities have long held competitive strengths in liveability. The 2010 ADC Cities Report: Enhancing Liveability describes liveability as a key part of "brand Australia", a critical element in attracting and retaining the brightest and best and in providing the basis for a high quality of life for all Australians, whether they live in cities or simply visit them.
Australian capital cities regularly feature in the top ten in international liveability rankings. However, the refreshingly honest federal State of Australian Cities 2010 report noted a concerning tendency for some rankings to decline in recent years. The absence of cities of greater than 5 million among the top ranked cities in The Economist and Mercer liveability surveys is also notable.
Australia has seen a number of different population projections of late, with projected numbers for 2050 being successively increased to about 36 million, and even higher in some scenarios. A range of 26 to 40+ million population by 2050 is currently well within the range of possibilities, the former perhaps reflecting a policy decision to have zero net migration and the latter assuming a sustained very high migration level, possibly linked to an humanitarian decision regarding a growing intake of climate refugees.
In light of these numbers, should we be planning for cities of 8-9 million or aiming to redirect growth to new cities or smaller cities? Can we have better cities at the same time we have bigger cities? If we have bigger cities, must they be high density?
Professor Ed Blakely from The University of Sydney notes that, with the right linkages, cities of 250,000-300,000 people, either standing alone or as a substantially self-contained element within a wider city, can have the benefits of both scale and density to be competitive, without the detriment and burden related to larger populations.
The "city of cities" concept acknowledges population groupings of this scale, and urban planning is increasingly recognising the benefits of structuring larger groupings of population into modules of this size. This means that entirely new cities can get built with 250,000 to 300,000 people or parts of existing cities re-imagined around this sizing. 250,000-300,000 persons in large conurbations provide for a sense of spatial identity and boundary, while allowing each node to contain many aspects of urbanity, such as theatres, sports teams and large parks and gardens.
The logic of this suggests that "cities" of 250,000 to 300,000 people, embedded with meaningful densities (sufficient to support strong economic and social networks, with a high degree of walkability being a key indicator), the right elements of competitiveness and inclusiveness for a knowledge economy, and good accessibility both within the city and between other cities, should provide one focus for our future thinking about cities. Within larger cities, the modularity implied by this approach provides an opportunity to soften the consequences of size by thinking village/neighbourhood.