Parramatta's role as a second CBD has been cemented by the state government's long-term plan for the Sydney's future, which is less definitive about how growth will be distributed across the city's suburbs.

The government's metropolitian strategy signals its intent to build up Sydney's western centre over the next two decades, as the city grows by almost 1.6 million people.

But the long-awaited "roadmap" defers detailing how much of the burden of growth will be borne by specific areas until after the next election.

The Plan for Growing Sydney, released on Sunday, instead sets an overarching target of 664,000 new dwellings and 689,000 new jobs by 2031.

The city's population is expected to grow to almost 5.9 million in the same period.

Urban Taskforce chief executive Chris Johnson said the document contained less detail than the draft strategy, which included housing and employment targets for each Sydney region when it was released almost two years ago.

"Maybe numbers give too much focus for local communities close to an election," Mr Johnson said.

Exactly how the big-picture targets will be spread out across Sydney is instead expected to be set out in six draft sub-regional plans by mid-next year.

This will be guided by elements such as 28 "strategic centres", or areas identified as priority locations for employment, retail, housing and services that are each expected to support at least 10,000 jobs.

The Greater Sydney Commission, a new government body announced in June, will oversee the implementation the strategy across 41 local government areas.

Planning Minister Pru Goward dismissed as "speculation" the question of whether the commission would be granted the power to override councils, insisting it would be "absolutely focused" on working with local government.

"We're getting the ball rolling with an injection of $6.5 million to start work and to establish the Greater Sydney Commission over the next six months," Ms Goward said.

The commission, whose members and leadership is yet to be announced, will initially function as a ministerial advisory body "and next year we will turn it into a legislated body," she said.

David Borger welcomed the strategy and its focus on western Sydney, but said the government now needed to be held to it.

"The devil's in the delivery, not the detail," Mr Borger said. "And we need an engine to be able to deliver this great plan and that's got to be the commission."

Peter Phibbs, a professor of urban planning at Sydney University, said while he would have liked to see some affordable housing targets, omitting a breakdown of the other targets was less of an issue.

"As long as they turn up in the sub-regional plans and are realistic it should be all right on the night," he said.

The opposition's planning spokesman Luke Foley said it appeared unlikely the commission would be given sufficent scope to drive Sydney's strategic planning.

Mr Foley also highlighted population projections that showed the northern Sydney would grow by less than 200,000 people by 2031.

"The Liberals want to add a city the size of Adelaide to the population of Western Sydney but only a town the size of Bundaberg to the North Shore – that is not a fair sharing of the burden," Mr Foley said.