The planning gap is "extreme" ... Professor Richard Weller, UWA.

The planning gap is "extreme" ... Professor Richard Weller, University of Western Australia.

IN A scandal of national proportions, millions are missing. The worst of it is not the missing dollars (though that's a problem too), it's the missing people: about 35 million of them, to be precise.

These 35 million lost souls are the difference between the upper end of Bureau of Statistics projections for the population by the end of the century (62.2 million) and the number catered for by even the most forward-thinking of Australia's planning authorities (27.5 million). So where and how will the missing millions live?

Richard Weller, the director of the Australian Urban Design Research Centre at the University of Western Australia, wants to know. The planning gap is ''extreme'', he says.

''All our planning documents only address a total of about 5 million extra Australians'' beyond the current population of 22 million-plus, and no capital city has plans beyond 2031 except Adelaide (2041), he says.

The 39.6 million extra people in the highest ABS projections (which Professor Weller argues prudent planners should use) is the equivalent of 115 Canberras.

Mega-regions are the solution he proposes in a forthcoming book for UWA Press, which he has written with his colleague Julian Bolleter. These are massive urban conurbations of more than 20 million people that, according to a 2010 UN report, are the ''new engines of global and regional economies''. They already account for 18 per cent of the world's population - and 66 per cent of its economic activity.

Australia should be planning for two of them by mid-century, the academics argue: from Brisbane to Melbourne on the east coast, with about 35 million people, and from Busselton to Geraldton on the west coast, with 10 million to 11 million people. National broadband and high-speed rail are ''absolutely critical'' to knit them together as cohesive economic units, according to Professor Weller.

The NSW Planning Minister, Brad Hazzard, said ''the planners are right to raise concerns about planning for growth''. A focus on infrastructure to back growth had been absent in NSW but is ''now the name of the game'', he said.

The academics want government to start setting aside land for new and expanded cities every 100 kilometres from Sydney to Melbourne, incorporating existing regional centres and three new cities with 23 rail stops in total. ''The most isolated citizen would be worst-case two hours from a major city,'' Professor Weller said.

There are already 40 mega-regions in the world, including ''Bos-Wash'' (Boston-Washington, 50 million people) and ''Hong-Zhen'' (Hong Kong, Shenzhen and Guangzhou, 120 million people).

One working definition for a mega-region is that it can be seen from a satellite image at night as a continuous illuminated area.

The Economist Intelligence Unit ranks four Australian cities among the world's top 10 most liveable cities: Melbourne (1), Adelaide (5), Sydney (6) and Perth (8). But the average population of the top 10 is only 1.7 million, so our capitals are unlikely to hold their places as the national population grows towards 42 million by the middle of the century, the authors argue.

Though population projections depend on assumptions and the reality may be different, it is ''irresponsible of any government, state or federal, to not have a serious and robust set of policy arrangements'' planning for such growth, said Jago Dodson, the director of the urban research program at Griffith University.

The first multi-government national urban policy was attempted last year but has fallen off the agenda since its release by the federal Minister for Transport and Infrastructure, Anthony Albanese, Dr Dodson said.

The first stage of a federal government-funded study into an east coast rail network also released by Mr Albanese last year put a price tag of $61 billion to $108 billion on a line linking Brisbane, Newcastle, Sydney, Canberra and Melbourne.