In 2010, filmmaker Warwick Thornton made an off-hand remark to a journalist, suggesting that the Southern Cross was morphing into a racist symbol — like the swastika.

"People got very upset, and that scared the hell out of me," he says.

"I went and hid in the cupboard for a little while, and then over a couple of years, I got angry."

Thornton has crystallised that simmering rage into something constructive — a documentary film, and a deeply questioning essay on what is sacred.

We Don't Need A Map is a punk-infused road trip into the history of the Southern Cross in both popular and Indigenous culture — "a delicate subject", according to Thornton.

The documentary — which premieres at the Sydney Film Festival this week — features lucid and often compelling commentary from an almost entirely male cast, that includes an astronomer, a philosopher, a slam poet, a rapper and a tattoo artist – all speculating on the use and abuse of the Southern Cross.

Where did the Southern Cross come from?

A stylised version of the Crux Australis constellation was mapped in a flag — reputedly designed by a Canadian — and raised during the Eureka Stockade rebellion, a miner's uprising against exorbitant government taxes and overregulation on the Victorian goldfields in 1854.

The tattered and torn Eureka flag raised during the miner's uprising in Ballarat in 1854. ( Supplied: Barefoot Communications )

More recently, the Southern Cross tattoo has become a visual metaphor for a particular kind of fervid, overheated Australian nationalism, like that which spilled onto the beach at Cronulla in 2005.

"When I first saw a Southern Cross tattoo years and years ago, pre-Cronulla, pre all the bullshit, I thought it was quite cool", Thornton says, contrarily.

Just as the swastika — a Hindu symbol — was colonised and debased by the Nazis, so has the Southern Cross been appropriated by extreme right-wing nationalists.

"It was hijacked by a bunch of dickheads," Thornton says.

In a risky move, Thornton — who won the Camera d'Or at the 2009 Cannes Film Festival for his uncompromising debut feature Samson and Delilah — decided to go on camera for this new film as the presenter.

Director, writer and cinematographer Warwick Thornton also presents this film. ( Supplied: Barefoot Communications )

The result is an anarchic, sometimes slightly comic journey, that goes from the glassy, green waters of north-east Arnhem Land via the red dunes of central Australia, to the pubs of inner-Melbourne.

Emu tracks and a cosmological map

An idiosyncratic but natural presenter, Thornton travels the length of the continent to find deeply-embedded stories of creation and belonging that go beyond the latter-day colonisation of the skies.

It has to be said that the real juice in this male-oriented film is the testimony of a cast of senior Yolngu, Warlpiri and Wardaman law men — each of whom are 'bosses' for their country.

In north-east Arnhem Land, Thornton meets Yolngu elder, the Reverend Dr Djiniyini Gondarra, who explains that the five stars are not a cross at all.

Rather than a cruciform as it might appear to Western eyes, the stars might be a track left by the emu in the nearby Coalsack nebula, which figures so much in Aboriginal cosmology.

A toy that features in the documentary, gazes up to the Southern Cross. ( Supplied: Barefoot Communications )

They might even be points on the journey of an ancestral canoe — a cosmological map.

There are many recurring themes in We Don't Need A Map — and in unearthing the hidden, or secret aspects of the meaning of the Southern Cross, the film is often serendipitous and surprising.

In certain Aboriginal cultures, the Southern Cross is associated with male initiation.

As a night sequence filmed on Warlpiri land in central Australia unfolds, it becomes clear that the constellation is a site of power, reverence and secret knowledge — not matters to be trifled with.

Along the road trip, just south of Katherine, we meet the Wardaman elder Bill Harney, who explains the significance of the constellation in the painted, cave-like shelter of a rock art gallery.

He says the ancestral beings, the 'sky boss' Nardi and his wife Dungdung, populated the earth and left clear instructions about the use of totems — and the clan designs to be worn on the body during ceremony.

"You can't steal another man's painting. You've got to have your own," Bill Harney says.

Cut to a tattoo studio in inner Sydney where the proprietor spins an unlikely yarn, about the derivation of the word 'picture'. The Picts, he says, were a Scottish tribe who were heavily tattooed.

A spike in tattoo removals

Another tangent in the story arc of We Don't Need A Map follows a former surf lifesaver as he undergoes laser removal of a Southern Cross tattoo.

The clinician performing the procedure tells the camera that there's been a surge in the number of clients wanting to have theirs removed — due to embarrassment.

A supporting cast of experts from historian Bruce Pascoe, social theorist Professor Ghassan Hage, rap artist Briggs, slam poet Omar Musa and creative director Dee Madigan bring a wide range of opinions to the question that beats at the heart of this film: what is sacred, and to whom?

Another toy featured in the documentary. ( Supplied: Barefoot Communications )

Big Day Out Festival promoter Ken West also makes an appearance.

In 2007, West's decision to ban the Australian flag at the festival after it was used as a pretext for violence and racist abuse - and occasionally as a sick bag - was ridiculed by the conservative media.

But the most lucid commentary comes from the Goenpul and Bundjalung philosopher, filmmaker, performer and cultural critic Dr Romaine Moreton, who for Thornton has become a sort of oracle.

"She's my go-to professor of the universe, she's just a revelation every time I talk to her," he says.

Thornton says he learned a lot during the making of We Don't Need A Map — and with each film he makes, he learns more about how to be a "better blackfella".

Surprisingly, he has even moderated his view about those who he once eyed with deep suspicion.

"The irony is, after making the film, I won't judge that book by its cover any more. Hey, I might even get a Southern Cross tattoo."