'I often use my imagination because it brings my film appreciation to a new level,' he says, pointing to a cluster of luxury flats on Conduit Road, which once served as the premises of the Foreign Correspondents' Club and stood in as a hospital building in the 1955 classic Love is a Many-Splendored Thing.

'The two leads [William Holden and Jennifer Jones] take a walk together to the hilltop from the hospital. Although the film didn't show the route, I found clues from the dialogue and recreated the walk here,' Ng says. 'It's fun and rewarding to share that romantic moment in the film this way.'

Although he prefers to keep his background low profile, even publishing his Chinese-language guide under the pen name Kei Fu, Ng shows an extensive knowledge of Hong Kong movies, accompanying his photos of the sites with detailed descriptions and lively commentary.

There's often more to the sites than meets the eye, he says.

'It's a personal journey packed with memories and discoveries. Navigating through the streets with film locations as lamp posts, one can recall the good old days of Hong Kong that were recreated in a particular movie to compare the discrepancy between life and art, reinterpreting the relationship between man and space,' he says. 'This sort of reconstruction and redevelopment are processes that never stop in this city.'

Ng fell in love with movies while studying business at Chinese University and used to watch Hong Kong movies whenever he could while pursuing an MBA in Montreal in the late 90s.

The idea of cataloguing film locations came to him about nine years ago. But the sheer enormity of the task kept him from attempting it until about four years ago, when he was immobilised for three months while recovering from an illness.

'I had nothing to do but watch movies at home and decided to give it a try,' he says.

Ng embarked on the painstaking project on his own, without help from film industry insiders or experts. He watched every movie on his list at least twice, taking snaps of key scenes and filing them in a notebook for future identification, usually during weekends free from work.

'It's like a field trip every time. It might be time-consuming, but that doesn't bother me because I'm doing it for myself. I like to wander and get lost in the city,' says Ng. 'I've always had good street sense and visiting film locations often takes me to parts of the city I haven't been to before.'

Ng, who recently created a blog (hkmoviewalker.blogspot.com) to share his discoveries, says he found many sites by chance.

For example, he traced to Central a doorway that formed the backdrop for a scene in Wong Kar-wai's Days of Being Wild, in which the policeman played by Andy Lau Tak-wah consoles a heartbroken Maggie Cheung Man-yuk.

'I thought it had gone. Then I came across it outside the Old Bank of China Building,' he says.

Although he was unable to confirm this with a secondary source, Ng went to great lengths, comparing details on the clock face and brick placement to film stills, before coming to his conclusion.

When Ng shared his observations in a weekly column for Ming Pao about two years ago, they caught the eye of Joint Publishing senior editor Angela Law Tsin-fung, who encouraged him to write the book.

'I admire his vision and perspective on Hong Kong movies,' Law says. 'He also takes his work seriously. For example, he insists on visiting the sites at the time of day depicted in the film - if it was shot at night, he would go at night to capture the essence of the place.'

The book highlights memorable movie moments shot in diverse locations from nightlife areas such as SoHo (Chungking Express, 1994; Confession of Pain, 2006) and Lan Kwai Fong (He's a Woman, She's a Man, 1994; The Beast Stalker, 2008) to now demolished landmarks such as Queen's Pier (The Romancing Star, 1987) and obscure corners in North Point (Infernal Affairs, 2002) and Shau Kei Wan (Lost in Time, 2003).

'For me, the location is as important as the characters,' Ng says.

Each well-researched chapter in the guide lists films shot at the site, accompanied by Ng's musings and anecdotes and a location map.

'This odyssey is about connecting the dots, having encountered many inspiring publications, people, and places,' he says, citing Wan Chai and Sheung Wan as his favourite locations because of their rich history and vibrant community.

'I'd like to produce a comprehensive book that shows how Hong Kong has changed in some of its defining moments over the past three decades,' he says. 'There are many foreigners who are just as eager to write about these places, but I'd like to write for Hongkongers by addressing the local history.'

Inspired by books such as Scenes from the City: Filmmaking in New York, Ng says he is impressed by how movies can help promote and celebrate a city.

'When I visited London, I was amazed by the way they promote the city using famous quotes from movies, showing them on billboards inside the Tube. Not to mention the effort spent by the government on Web pages dedicated to film locations,' he says.

Ng hopes his book can fill the void left by the Film Services Office's online location library, which has yet to systematically document such material. Next on his schedule are guides to film locations in Kowloon and the New Territories, although he acknowledges that even his first guide is by no means a complete record of locations on Hong Kong Island.

His efforts are hampered by limited time, resources and knowledge, Ng says, but his biggest problem is the rapid disappearance of many landmarks and sites due to frenetic redevelopment.

'Over the past few years, there has been an increase in local movies being shot on location because filmmakers are more realistic and pay more attention to detail,' he says. 'But Hong Kong movies need to be shot in interesting streetscapes, not shopping malls. I'd better hurry up to capture them before they're wiped out.'