In your palm, memories of horror and valour

The city of New York is not meant for memorials. In a city where everything lurches relentlessly into the future, who has time to mourn the past?

The problem of how - or whether - to enshrine memory is especially clear at Ground Zero, where after almost a decade the official memorial is nowhere near completed and the feelings of many New Yorkers are nowhere near resolved.

But what to do with those unresolved feelings? Go to the World Trade Centre site and take pictures? Watch the somber annual remembrance on TV? Just in time for the ninth anniversary, the design firm Local Projects, working under the aegis of the 9/11 museum-to-be, has come up with a much more satisfying option. And it comes, of all things, in the form of a free iPhone app.

The Explore 9/11 app, which has already been downloaded 100,000 times, is a guided tour around the perimetre of the World Trade Centre site, narrated by the people who lived through it all.

Small enough to fit in the palm of your hand, the app is as different as could be from the grandiosity of most memorial projects. But that same reduced scale makes it feel much more personal, and therefore much more powerful. Instead of reading quotations inscribed in granite, you are listening as someone whispers them in your ear while you cradle the phone and strain to hear more.

(Actually, straining to hear is a serious problem: imagine having a phone conversation at the edge of the biggest construction site in the city and you'll get a sense of the challenge. Ear buds or good headphones might help in this regard, and would in any case let you actually look at the accompanying photographs while listening.)

After a brief introduction, the tour begins at the corner of Vesey Street and West Broadway, where someone named Bruno Dellinger recalls the moment of impact. Having heard many such narratives, and perhaps having 9/11 stories of your own to tell, you might think these accounts had lost their power. But Mr. Dellinger's -- delivered in plain language, without any rhetorical flourishes -- is pure shock and awe.

Next, Mary Hagen, who walked down 81 flights of stairs while eight months pregnant, talks about the police officer who escorted her out of harm's way. "He just drove down by City Hall, and that's where he let us out," she says. With a tone of just-dawning wonder, as though comprehending his sacrifice for the very first time, she adds, "And then I think he went back."

I listened while standing among a bunch of construction workers taking a coffee break. Behind them, members of New York's Congressional delegation were demanding health care for 9/11 first responders. And one block beyond that stood the site of the proposed Islamic cultural centre, the unnoticed eye of a national storm.

At the pedestrian overpass on the corner of Vesey and West Streets, Lt Joseph Torrillo of the Fire Department talks about realising that the towers were about to collapse and ordering all the emergency vehicles to evacuate. Seconds later, his prediction came sickeningly true. "I figured," he recalls, "if I made it underneath that bridge that goes over West Street, I said, well, maybe they'll find my body." They did find it - somehow alive despite having been hurled against a wall and battered by steel and concrete.

Not all the testimonials are quite that vivid. Over all, however, the presentation is admirably accessible and straightforward, easy to navigate and easy to adjust to your own pace. If it's suddenly too much, step into a newsstand and read some magazines, or disappear into the eerily pleasant Winter Garden of the World Financial Center.

When you're ready to go again, just hit Play. (There are other 9/11-related apps -- a four-minute tour of historic Lower Manhattan, a panoramic view from atop the World Trade Centre and a slideshow made by a designer whose other apps include "How to Fart" -- but there is nothing of comparable depth.) Explore 9/11 also offers an interactive timeline and a map of photographs submitted by ordinary citizens and displayed, thanks to the GPS reading on your cellphone, according to their proximity to the spot where you're standing.

These features are less successful than the tour. For one thing, they rely on the never-all-that-satisfying Google Maps interface, with its dense cluster of bulbous pins. For another, the information used to classify the photographs is only as accurate as the people who took them. Finally, of course, the whole thing happens on a cellphone. Standing on Vesey Street, I was all but unable to get the photos to load; they crept in at a snail's pace until I gave up in frustration.

When it works, though, the effect is beautiful and haunting. Load a photo taken nine years ago on the exact spot where you are standing. Position yourself or your phone so you have the exact same perspective as the person who took the photograph did. Now, shift your eyes from despair to regrowth and back again, and think about how much can change in a decade, or a day.

It's this effect -- layering past over present, present over past -- that makes Explore 9/11 such a good fit with the city it memorialises. In New York, nothing stays still but nothing entirely disappears. Anyone who's lived here long enough to regard someone else as a newcomer knows the apartment that was torn down to make room for that ridiculous hotel, or the electronics repair shop that preceded the organic-babywear boutique. Allowing the city of grieving memory to coexist with the city of current growth, and placing them both within the palm of your hand, is a powerful way to focus a New Yorker's attention -- for a moment, until it's gone again, lost in a rush of delirious amnesia.