There may be a simple explanation why Australian cities are consistently ranked among the world's most liveable cities — they are not that big.

World's most liveable cities Rank Rating Melbourne 1 97.5 Vienna 2 97.4 Vancouver 3 97.3 Toronto 4 97.2 Calgary 5 96.6 Adelaide 5 96.6 Perth 7 95.9 Source: Economist Intelligence Unit

The Economist Intelligence Unit's 2016 report ranked Melbourne as the number one city for the sixth year in a row, while Adelaide placed equal fifth and Perth was seventh.

While some Australians took to social media to crow about the cities' achievements, others questioned how the state capitals could compare to major metropolises such as New York, Paris and London.

"The fact that both Perth and Adelaide are also in the top 10 shows what a sad state of affairs the world is in. Boring must've been big in the criteria," Facebook user Josh Booth commented on the ABC's story.

"Need public transport as awesome as Japan or London!! And affordable housing. But love my Melbourne," Kerry Cameron wrote.

Green spaces highly prized

The EIU scores the cities on a number of factors — healthcare, stability, culture, environment and infrastructure.

However, according to the experts, size matters.

Laurel Johnson, an associate lecturer at the UQ School of Geography, Planning and Environmental Management, said there were few other major cities that were still small enough for residents to get a house "with a yard, some chickens a dog that is still within a commutable distance to the CBD where they could work white collar jobs".

She said Melbourne's relatively low population density, range of housing options, culture and focus on green spaces, made it an easy pick for the world's most liveable city.

Melbourne's focus on green spaces helped it best other cities, according to experts ( Supplied )

Professor Douglas Baker from QUT's School of Property and Planning agreed a city's liveability often boiled down to the size of its population.

He pointed out that the only European cities in the top 10 — Vienna, Helsinki and Hamburg — were not large on a global scale.

"Once a city expands to a certain size then a variety of things happen. One, affordability is hit," he said.

"Secondly transportation [is] a major area of entry to the job market so people are commuting — and that's not liveable when people are commuting an hour each way. That's two hours a day.

"So affordability, commuting time and pollution — they all sort of circle around the same areas."

New York has become a victim of its own success. ( Reuters )

Professor Baker also noted Australia's health, infrastructure and education, which he said compared well to the rest of the world.

The EIU also made the link.

"There does appear to be a correlation between the types of cities that sit right at the very top of the ranking," the report said.

"Those that score best tend to be mid-sized cities in wealthier countries with a relatively low population density.

"These can foster a range of recreational activities without leading to high crime levels or overburdened infrastructure.

"Six of the top 10 scoring cities are in Australia and Canada, which have, respectively, population densities of 3.1 and 3.9 people per square kilometre."

Lower crime in smaller cities

Sydney, which ranked seventh last year, dropped out of the top 10 due to a "heightened perceived threat of terrorism", according to the report.

Sydney is now out of the top 10 ( Getty Images: Todd Warshaw )

However, it noted the crime rates in the top 10 cities were low compared with the global big smokes.

"Global business centres tend to be victims of their own success," the report said.

"The "big city buzz" that they enjoy can overstretch infrastructure and cause higher crime rates.

"New York, London, Paris and Tokyo are all prestigious hubs with a wealth of recreational activity, but all suffer from higher levels of crime, congestion and public transport problems than are deemed comfortable," the report said.

"The question is how much wages, the cost of living and personal taste for a location can offset liveability factors."

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