If you've seen those ads the mining industry is running you probably realise the entire economy is riding on the miners' backs, and if asked to pay another dollar more in tax they'll up sticks and shift their mines to some better-run country like Peru or Nigeria.
If you've spoken to a farmer any time in the past 50 years you'll know it's actually farming that's propping the economy.
In either case you'll be surprised to know the truth: according to estimates by the Department of Infrastructure and Transport, 80 per cent of Australia's economic activity takes place in Australia's major cities.
That's because the great majority of us live in big cities. We live there because that's where most of the jobs are. Equally, most of the jobs are where the people live because most jobs involve doing things for people (such as bringing them the news).
But it's not by accident that so many of us happen to be piled into a handful of cities (as are people in all developed countries and, increasingly, many developing countries). We pile together because it's more efficient economically, thus making us more prosperous.
For one thing, it saves on transport and other distribution costs. For another, outfits such as hospitals and schools - even shopping centres - gain economies of scale when they have more people to serve.
But that's just the start of the "economies of agglomeration", as Jane-Frances Kelly and Peter Mares point out in their report for the Grattan Institute, Productive Cities.
We're used to dividing up the economy by sector - agriculture, mining, manufacturing and the big one, services - and focusing on how these sectors' shares of the economy are changing. But this blinds us to an important development.
"One of the most significant long-term shifts in advanced economies is towards knowledge-intensive activities. These take place across all sectors of the economy," the authors say. In other words, there are knowledge-intensive jobs in each of the sectors - but almost all of them are located in the cities.
Knowledge-intensive activities tend to involve customised problem solving, which requires significant intellectual effort. So such workers solve problems and generate ideas. Their jobs are clean, safe, well-paid and intellectually satisfying. They're the way for Australia to go if we want a better future than just farming and mining (lucrative though they are).
But here's the point: knowledge-intensive activities grow best in big cities. This is because people and businesses learn from each other, and the closer together they are the more they learn. According to the urban economist Edward Glaeser, the "central paradox of the modern metropolis" is that even as the cost of connecting across distance falls, so the value of being close to other businesses rises.
As well, the more businesses and workers cluster together, the more they each benefit from "deep" labour markets. Firms have more workers to pick from; workers have more firms to pick from. Jobs can become more specialised, and ever-increasing specialisation is one of the main ways economies have become richer over the past 200 years.
When you specialise in something you get better at it. And the individual worker more closely fits the needs of the individual employer (which makes the worker more valuable and able to command a higher salary). But the more specialised you are the more contact you need with others in your specialty to help you keep up.
The report says that, adapting to changing economic circumstances, Australia's largest cities have evolved from compact colonial cities where jobs and houses were close together and most people walked to work, to cities that spread outwards into suburbs.
"This transition was made easier by changing transport technologies: first trams and trains, then buses and cars. The transition further separated the worlds of work and home, an arrangement that was well suited to a 20th-century economy driven largely by manufacturing, when industry could often be a dirty and noisy neighbour."
Initially this led to the "hollowing out" of inner cities as both residents and jobs moved to the suburbs. In the decades since 1980, however, the trend began to turn around, as services began to replace manufacturing as the main source of new jobs.
Combined with factors such as traffic congestion and rising fuel prices, this helped to prompt a resurgence of CBDs and inner suburbs as places to live and work.
The point here is that the economic efficiency of cities - their ability to generate well-paying jobs - turns on where the jobs are, where the homes are and the adequacy of the transport system that allows us to move between the two.
But the report finds that labour markets are shallow in significant parts of Australia's biggest cities. "In many suburbs - particularly outer suburbs - residents can reach fewer than 10 per cent of all metropolitan jobs with a reasonable commuting time," it says.
The answer is not for governments to try (and often fail) to create jobs in outer suburban areas. People want to live closer in, and many of them want units rather than houses. So the answer is to remove the disincentives faced by developers building in established suburbs and stop established suburbs from being "locked down" by restrictive zoning and planning rules.
The way to reduce traffic congestion and increase the capacity of city transport systems is to start charging for the use of roads and use the revenue to expand public transport.
