Can your suburb help fix Australia’s housing crisis? It all comes down to density

Photograph: Charlie Rogers/Getty Images

Skyrocketing rents and a projected home shortage have sparked fierce debate on the most effective ways to address Australia’s housing crisis.

Experts say one of the most effective fixes is to increase the supply of housing, specifically infilling urban areas to increase the density of areas where people actually want to live.

Exclusive data provided to Guardian Australia by the United Nations shows Australian cities are well behind many others globally in terms of population density – there are hundreds of cities around the world that are more dense than Sydney or Melbourne.

Australia has added millions of people and dwellings over the past decade, but the data shows increased density is mainly concentrated in a few areas – around city centres, and especially in Melbourne and Sydney.

Twelve of the Top 20 suburbs with the largest increases in population density over the past decade were in metropolitan Sydney. Led by Wentworth Point in Sydney’s west and Zetland and Waterloo to the south of the CBD. Southbank to the south of Melbourne’s CBD was third and Newstead in Brisbane was fourth.

You can explore density in Australian major cities by searching for postcodes in the map below.

Guardian Australia combined census data from 2011, 2016 and 2021 to identify changes in population and dwelling density over the past decade. Both density measures were calculated in square kilometres.

Census data can be slightly problematic as it relies on snapshots in time – it’s all collected on one night. The 2021 census was also conducted during the pandemic, when many temporary migrants had left Australia, some Australians were stuck overseas, and we were all attempting to find more space. Some boundaries for suburbs and those used for data collection have also changed slightly over the decade.

Dr Elek Pafka from the University of Melbourne notes that the census is also affected by the season it’s held. “The census for instance is usually around August, which is winter. This means that [the density of] places that have higher populations in summer because of tourism is not captured.”

But the number of physical dwellings should be relatively stable, and it’s quite noticeable when you compare population and dwelling density that the areas don’t always match.

The maps also show how some city suburbs are attracting more population than others. There were 9,000 more people living in Zetland, in metro Sydney, in 2021 than there were in 2011.

In Kensington, the suburb right next door, there were actually fewer people counted in the 2021 census than there were in 2011, despite almost a thousand more dwellings.

Hunters Hill, on the other side of the harbour, has an almost identical population in the 2021 census as in 2011 (it was slightly higher in 2016, pre-pandemic). But only about 300 more dwellings were added over the 10 years.

Density in many suburbs along the Sydney harbour including Elizabeth Bay, Rushcutters Bay and Millers Point went backwards over the ten years. The same happened in Carlton North and Flemington in Melbourne’s north and north-west.

Dr Pafka says a lot of the differences in density across cities and time can be partly explained by changing household composition and changed housing.

“People have less children now. So that’s one reason for changed densities in areas like Elizabeth Bay. In the same apartments 100 years ago, there were families of four or five people and now it’s perhaps just one person.”

Many of the densest suburbs in Australia are in Sydney. This is because Sydney has the most densely populated residential area.

Dr Pafka says this is due to the areas surrounding the city.

“Sydney has effectively created a green belt by declaring national parks all around it. So the national park in the south, Blue Mountains in the west, Ku-ring-gai in the north.

“So basically, [Sydney] doesn’t sprawl that much, as compared to Melbourne that, through planning systems, had green belts that were constantly shifting.”

But even though Sydney has the greatest density in Australia, it is far from the most dense internationally. Based on data from UN-Habitat, there are at least 80 cities that both have a greater population than Melbourne and Sydney, and are also more densely populated.

This data identifies the boundaries of cities based on contiguous densely populated areas. It also excludes open water from the land area and only uses built up surfaces. It tries to identify more of what housing experts call “intensity” of life rather than just density.

In this measure, Sydney and Parramatta are considered separate cities. As are Melbourne and Werribee. The most dense cities in the world are Hong Kong, and Mumbai and Surat in India.

That Melbourne recently overtook Sydney in terms of total population, shows the way we measure cities heavily influences how populated they are. Depending on how you define “Sydney”, it can range from just over 400 people per sq km, to almost 8,000.

“There’s this statistical kind of artifice that the way you define a metropolitan area will have an influence on the data you find,” says Dr Pafka.

“At some point, Melbourne and Geelong will be continuous and [Geelong] will become part of Melbourne. Then Melbourne’s population will really jump up without the current Melbourne growing or densifying.”

Notes and methods:

Population and dwelling over time calculated from 2011, 2016 and 2021 mesh block counts.

2011 and 2016 data was corresponded to 2021 boundaries before being divided by the Albers area for 2021.

Areas with zero population or dwellings in 2021 were dropped from the calculation.

UN population and land area data based on the Global Human Settlement Layer.

UN-Habitat identifies urban centres as cities with more than 50,000 inhabitants with a continuous population density above 1,500 inhabitants (based on satellite data).

UN-Habitat identifies as the built-up surface (buildings) in km² excluding open water.