The Department of Planning and Infrastructure this week released figures showing the Sydney and NSW populations were growing much faster than predicted only two years ago.

When the government's previous population projections were released in 2014, the population of Sydney was expected to be 6.25 million in 20 years, up from about 4.3 million in 2011.

The government's updated forecasts show the city is expected to have about 6.42 million in 20 years – 170,000 more than predicted only two years earlier.

But a breakdown of those figures shows the increase in the expected population is not spread evenly across the city.

Of those 170,000 more people, 35,900 are expected to reside in Canterbury. Almost 26,000 are expected to reside in Parramatta, 25,000 in the Hills in Sydney's north west, and 23,000 in Camden in the south west. The increase also included 18,850 in the City of Sydney.

And in some areas of Sydney, the expected population actually fell between the 2014 projections and this year's.

Those areas include Fairfield, which was earlier expected to grow to a population of about 240,000 in 2031, but is now expected to grow to only 221,000 – a difference of about 19,000.

In the Sutherland Shire (15,700), Warringah (14,950), and the Blue Mountains (10,350) the expected population increase also slowed in the past two years.

Interviewed about the updated projections, Planning Minister Rob Stokes said the housing supply in Sydney needed to change, but that change needed to be managed in a way that was fair.

For instance, Mr Stokes said heritage characteristics of some suburbs should be preserved. "We have to be careful in developing in these areas, because there's a lot about Sydney you would want to keep.

But he said "we've got to be a just city."

"We can't just create pockets of privilege just because. There has to be good reasons in the wider public interest as to why areas need to be shaped appropriately and respectfully. And part of that is respecting heritage."

Mr Stokes also made clear his preference for the types of new dwellings he'd like to see in many suburbs – those being smaller projects such as terrace housing or smaller apartment lots.

The Committee for Sydney, an advocacy group, said Sydney had the potential to host a variety of new dense places.

"These places will be mixed-use, with different types of people bumping into each other," said the chief executive of the Committee for Sydney, Tim Williams. "They'll also have walkability at their heart – you'll be able to walk to the shops and the park in five minutes," said Dr Williams.