Wednesday, 14 August 2013

The size of Australian cities: urban sprawl graphed

The dense core of Melbourne CBD
The dense core of the Melbourne CBD

What is Australia's largest city? That's not a trick question. The answer is the obvious one: yes, it’s that big city on Sydney Harbour.

Sydney is the largest city simply because it has the most people, with 400,000 more people than Melbourne according to the 2011 census. However, population is not the only measurement that counts; it’s also interesting to look at the physical size of a city.

In this chart we have measured the physical size of Australian cities by looking at the spread of residents across their land - in essence by charting its change in density.

The graph above represents a north-south dissection of each state capital. It opens up the anatomy of each city in terms of how many residents are squeezed into its space relative to distance from the CBD. 

It uses the capital city boundaries defined by the Australian Bureau of Statistics (ABS). Therefore adjacent places such as Lake Macquarie, Newcastle, Geelong, Gold Coast and Sunshine Coast are not included (see here for maps). They do include, however, the Central Coast in their boundaries for Sydney, the Mornington Peninsula for Melbourne and Mandurah for Perth.

So what does the chart tell us?

Surprise, surprise: Sydney is the largest city in Australia. It also tells us that Sydney is consistently more dense than Melbourne across most distances. It shows the degree to which Sydney's northern sprawl adds to its population. The northern half of Melbourne Stops after about 47km, whereas Sydney extends to almost 90km in that direction. We can also see, however, that Melbourne's southern stretches further than that of Sydney.

Some other interesting things can be gleaned from the graph. Perth's notorious sprawl shows up with its southern side extending beyond Sydney's. All of the Australian state capitals generally follow a bell curve shape, with densities tapering out gradually. This indicates that interference in terms of regulations, NIMBYs or geography isn't a huge factor.

Taller points on the graph mean more people are squeezed into a smaller space, and shorter points are where people are more spread out. Unsurprisingly, we can see that as we move out further into the suburbs, people become more spread out. This is the Australian Dream in data.