For some people, the inner city means the area where cafe society thrives – probably a 10 km circle around the CBD in cities like Sydney and Melbourne. Or it might mean the extent of medium density historic terrace housing.
Some Brisbanites think of the inner city as the large area covered by the Brisbane City Council (1,367 km2) while some Melburnians think of it as the area serviced by tram lines.
Planners have addressed this problem by adopting simple measures. For example, in Melbourne the inner city is customarily defined as the area covered by the central municipalities of Melbourne, Yarra and Port Phillip (77 km2). Sometimes the Prahran portion (SLA) of the City of Stonnington is also included.
In my work on Melbourne I define the inner city as the area (79 km2) within a 5 km radius of the City Hall . This approximates closely to the three inner municipalities, but I use it because it’s consistent with what’s done elsewhere. US researchers typically use a 3 mile radius to define the inner city – an area approximating the size of the central Counties of the larger metros.
There are a number of problems with this sort of ‘administrative’ approach. A key one is that there is no underlying rationale for where the boundary is drawn – why not 2 km or 10 km? Another is that it doesn’t really connect with people because it has no obvious reference like, say, the tram network.
It would be helpful in managing our cities if we were to have a commonly accepted definition of the inner city. Here are some possible dimensions that we might use to define it objectively:
- Dwelling density, lot size and dwelling form
- Population density
- Morphology (measured, say, by walkability)
- Socioeconomic, cultural, political and demographic profile
- Transport infrastructure
- Historical period of development
- Mix of activities, e.g. ratio of population to jobs
- Linkages with the CBD, e.g. proportion of workforce working in the centre
Many of these aren’t very stable. For example, you only have to go back 40 years to a time when the socioeconomic composition of inner suburbs was vastly different to what it is now. Some don’t compare well across cities – Sydney and Melbourne might have terraces but they’re rare in Brisbane, where housing was always detached.
Population density is also a questionable measure. Smaller household sizes associated with gentrification mean some suburbs close to the centre have population densities that are much the same as those of fringe suburbs. And dwelling densities are on an upward path across large parts of our cities, most especially in Sydney.
I like the idea of something simple and enduring like the area of settlement circa 1900. It approximates the urban form of our major cities before the advent of trains and trams led to wholesale suburbanisation. Similarly, the extent of settlement around 1950 describes our cities before cars completely changed the urban morphology.
This doesn’t amount to a “theory” but it is a stable way of defining different sub metropolitan regions. It is comparable across cities and unaffected by their different historical paths. It can accommodate the changing socioeconomic and social roles of regions and changes in their physical composition.
In fact it’s tempting to think that the term “inner city” is out-moded. We might be better off simply describing major parts of our cities by something like their historical epoch.
But I think there really is an area close to the centre that makes sense of the term “inner city”. It goes back to why cities exist – agglomeration economies. Density lowers the cost of moving people (for both work and ‘play’), ideas and goods.
Notwithstanding the growth of suburban centres, the CBD remains by far the largest centre of economic activity in virtually every city in the world (Atlanta is one of the rare exceptions). So the idea that the “inner city” functions in a way that is defined by its proximity to the CBD is an important one.
The accompanying graphic – which shows the density of jobs in Melbourne in 2006 by their distance from the centre – indicates two things. First, the CBD is an order of magnitude more dense than any other part of the metropolitan area. Second, employment density falls off very quickly after the first kilometre and is effectively flat by the four to five kilometre point.
So five kilometres, at least in the case of Melbourne, reasonably approximates the “inner city” when its economic function is used as the basis of the definition. As with my previous discussion of the definition of a city’s boundary (see here), this approach not only provides a consistent basis for defining the area of the inner city but is also supported by “theory”. Some other variables are also relevant, such as the proportion of the resident workforce that works in the CBD and the value of proximity to the centre for (non-economic) social or consumer interactions.
There would be value in having a wider discussion about how more rigour can be applied to defining cities and sub regions. We need to have a logical schema for defining not only the inner city but also other parts of the metropolitan area.