Several years ago, when film-maker Mira Nair headed to India to shoot the final scenes of William Makepeace Thackeray's Vanity Fair (2004, starring Reese Witherspoon), she wasn't looking for inspiration for her next project. She already had two meaty ones well underway - screen adaptations of Tony Kushner's play Homebody/Kabul and Hari Kunzru's novel The Impressionist. Nair only wanted a novel to fill the long hours of the flight and so she picked up a book she'd bought six months before but hadn't cracked. What happened next was one of those rare magical intersections between art and life where the two seem to inform each other so profoundly that they are no longer separate.

The book was Jhumpa Lahiri's novel, The Namesake, and Nair's screen adaptation of it is to be released this month. Nair recalls the book touched her so immediately and profoundly that when she landed in India she called to see if the rights were available. A week later the film was hers. The timing was such that Nair read it when "I had just lost my mother-in-law and was in mourning," she says. What she found was an immense solace. "It was like some sort of balm to be understood in my loss and also to be perceived in the see-saw of my worlds," she says referring to the migrating back and forth between India and the US that has marked her own life since she left India at 17 to study at Harvard.

Nair's adaptation of the novel is nothing less than faithful to Lahiri's story, and yet the film is inflected, if not imbued, with Nair's vision of the world as she takes on with great pathos and deft comic timing such resonant themes as parent-child relationships, the nature of "what is home" and how marriages work-or don't work for that matter. For viewers who have not had to split their lives between two continents, Nair is able to convey-in a shorthand akin to poetry-both the richness and the sadness that is inherent to this existence as the film moves back and forth between Kolkata and New York City.

Late one afternoon, I catch up with Nair at her office off Union Square in Lower Manhattan, a high-ceilinged loft space with blond wood floors and tall windows, decorated with posters of vintage Indian cinema and of her own films. Two assistants are at work when I come in and I am soon ushered into Nair's private office, which aside from the desk, has low, comfortable couches and colourful pillows giving it a warm, calm and vibrant feeling not unlike Nair herself. She greets me with a hug though we've only met once before. Outside, the pale, wintry sky over the landscape of rooftops makes the office seem all the more cosy as we talk over chai and dates that the actor Kal Penn has brought back from fans of hers in Saudi Arabia - though I suspect Nair could make the inside of a military cargo plane seem cosy! She exudes an unusual combination of easygoing warmth and focus that makes the rest of the world seem to fade temporarily, whether she is talking about film-making, family or creating gardens.

In putting together The Namesake, Nair says she thought of it as "a kind of flag to desi power". In addition to hers and Lahiri's contributions, there was her long time writing partner, Sooni Taraporevala, a cutting edge British-Asian musician named Nitin Sawney who did the music and all the actors and actresses. "We were everyone from everywhere, but we were all from one subcontinent," she says. One of her central challenges was handling the 30-year span of the story "and not lose gargantuan steps." The answer, Nair realised, lay in looking at the two cities, Kolkata and New York (which Nair used instead of Lahiri's Boston), and trying to visualise them as one.

This unifying of two seemingly distinct locales, she explains, "is the state of mind and state of heart of a person like me who lives between places. You look outside at the Hudson River and it could be the Ganges one day". Also, she adds, "There is a similar energy. Both cities are slaves of excellence." In terms of motifs, she finds "the bridges of both cities are extraordinarily and iconically similar", and once she realised she could use both bridges and trees to bring the cities together for the viewer, things began to move forward from there.