The volume of development across the city is remaking the way in which Sydney residents and councils conceive of the geography of their city.

And for the new City of Canterbury-Bankstown, the mega-council established through merger this year, the changing contours of development means Bankstown is now part of Sydney's south, not its west.

At the council's meeting on Tuesday night, administrator Richard Colley withdrew the area from the Western Sydney Regional Organisation of Councils. Explaining the decision, Mr Colley said the focus of WSROC had shifted further west.

"The major areas that WSROC are looking at are very much centred around the Nepean River," said Mr Colley.

Mr Colley said Bankstown had joined the Southern Sydney Regional Organisation of Councils as well as WSROC during his previous stint as Bankstown's general manager, which finished in 2007.

"Since then of course Western Sydney has grown, and although WSROC services all the individual LGAs [local government areas], the big issues that are facing WSROC at the moment are things like the Badgerys Creek Airport, the north south railway link, Hawkesbury to Campbelltown, flood mitigation of the Hawkesbury river, and rail lines linking the greenfield development sites in western Sydney," Mr Colley said.

"A lot of those really don't apply to us, or we only have very little interest in it," he said. A further factor was that Canterbury Bankstown had been placed in the "Southern District" by the Greater Sydney Commission, the organisation established this year to coordinate planning across the city.

In administratively breaking Bankstown from Sydney's west, the administrator is arguably reflecting changes well underway.

Bankstown's most famous son, Paul Keating, reflected a decade ago that the area had already become "relatively inner city."

"In my day, it was on the periphery of the sprawl," the former prime minister said in a speech.

But Sue Rosen, a heritage consultant who has written a book on the history of Bankstown, said she was surprised to hear about the break

"I always thought it was western Sydney, and I think everybody out there thought they were as well," said Dr Rosen.

Is Bankstown west or south? Photo: Google Maps

Bankstown, she said, started to emerge as a city after WW2, with the influx of migrant families.

"But people also moved there because the Georges River was pretty clean," said Dr Rosen. "There were resorts, pleasure gardens on the Georges River. It was still seen to be a pretty healthy place. People moved from the inner city out there to give their kids a healthier lifestyle," she said.

"I guess Sydney's heading further west and south-west… in some ways Bankstown with the train line, it is now looking closer to the city than we had previously perceived it."

The president of WSROC, Blacktown mayor Stephen Bali, was not impressed by Mr Colley's decision.

"Bankstown is an integral part of western Sydney," Cr Bali said.

Western Sydney University, for instance, has a campus in Bankstown. And the suburb remains a relatively short drive from Parramatta and Liverpool

"The disappointment on my part," said Cr Bali, "I just think you have one person, the administrator, making this type of decision, when literally in nine months time you will have a new council elected. This is more of a democratic council decision rather than an administrator decision," he said.

"Why would you want to jump out of a growing thriving western Sydney into a sedate side of the city?"