AUSTIN – Matt Green once walked from Rockaway Beach, N.Y., to Rockaway Beach, Ore. – 3,100 miles over a span of five months.

So thoroughly walking his home turf in New York City should be a snap, right?

More than five years and 8,571 miles after beginning his quest to walk every street in the five boroughs, he’s still walking. What he’s accomplished so far, though, is the subject of the documentary “The World Before Your Feet,” which made its world premiere Saturday at SXSW.

A few hours later, I sat down with Green and director Jeremy Workman to talk about their epic project:

I think some people might be surprised to learn that the cumulative mileage of all the streets in New York is about three times the mileage of a cross-country walk.

Matt Green: It’s like when you’re a kid and you read in a book that, like, if they pulled out your intestines and stretched them end-to-end, it would reach to Antarctica or whatever. That’s what the city feels like to me – all this stuff bundled up in this tight knot. But if you were to expand it and make it linear, it’s just insanely long.

Jeremy, you did a significant portion of Matt’s walk with him, only walking backward and holding a camera.

Jeremy Workman: And running fast to get shots! When I started shooting, I was thinking, “I’m just going to be filming a guy walking – it’s going to be super easy.” What I found really fast was that it was really difficult and challenging. Matt’s not waiting around for me – he’s got his own plans for the day, and he doesn’t want to stop while I adjust camera stuff. So it really forced me to be on my toes.

M.G.: Jeremy is amazing at holding a camera in traffic and somehow not getting hit by cars.

J.W.: It was a little bit like being a gymnast.

I’m sort of amazed that you didn’t buy a FitBit, just for your own satisfaction.

J.W.: I would look at my iPhone and go, “Damn – I just walked 15 miles with Matt, lugging equipment.”

Along the route, over the course of weeks and months and years, you started noticing these commonalities around the city.

M.G.: The barbershops (Editor’s note: Green as an affinity for store names that substitute letters – as in Kutz and Kurlz) and the 9-11 memorials, those were the two things that I thought from the beginning I’m just going to keep track of these things. … For me, [it was about] keeping track of two things that are of no commercial value – one of which is silly, and one of which is very emotional.

I thought it was interesting that you guys didn’t take a methodical approach to ticking off the blocks. You just walked the path you felt like walking on a given day.

J.W.: Yeah, it was very much in the spirit of what Matt is doing. Matt’s not trying to check anything off – for Matt it’s not a checklist. It’s a journey for him – he’s doing something that’s emotional and personal and it’s an experience, but it’s not about – to use a cliche – it’s the journey, not the destination. … Matt finds these things – these small details – that are personal, and it’s the details that reveal.

Matt, one of the observations you make in the film is the idea that we may live very near a street, but if it’s not on our regular route to work or another common destination, we may not know what’s happening so close to where we exist on a regular basis.

M.G.: It makes you question what it means to even know a place – to know a neighborhood. Does that phrase even have any meaning? You could’ve lived in a neighborhood your whole life and never been somewhere that’s a quarter of a mile away from you. So I think it just gives you a lot of humility that you’re just one little speck in this ocean of a city. Your experiences are important, because they’re yours, but they’re nothing compared to everything else that’s going on there. And I think that’s a really reassuring feeling in a way – it’s this endless mystery that you get to go explore every day, and you’re never going to get tired of it.

Was there anything unusual that you came across on a walk?

J.W.: One that really stands out that we decided not to use was tombstone beach. … Matt is walking along and I’m filming him and he realizes that  all on the ground are tombstones. And they’re discarded tombstones – mostly from the 19th Century or early 20th Century. It was very strange.

M.G.: It was a former landfill, and these tombstones were the last thing added to the landfill, I guess. … Something had happened to them at the cemetery, and they replaced them. A tombstone seems like a sacred object, but when you get a new one, you have to put the old one somewhere, and that is where they happened to be.

Do you look at the streets you walk regularly in a different way now?

J.W.: After making the movie, I can now walk any street in New York City and my mind is always blown. … I walk pretty slow now, because I’m seeing all these things that I never used to see.

Any other takeaways from the experience?

M.G.: You can’t really know anything about a city in a large-scale way. I think anyone who says, “Oh yeah, I’ve been to that city a bunch – I really know it.” That is a meaningless thing to say. I mean in a place like New York, where millions of people live with a variety of backgrounds, cultures, religions beliefs, political beliefs, economic backgrounds – this unbelievable diversity of humanity is there. And to think you can know anything about that, after this walk, seems like kind of an arrogant thing.