It questions what it means to have lived a life. It looks at the things we leave behind and it asks the question: 'If these things fade away or become unavailable, does that mean that the life wasn't lived?' It also looks at the need for some people to ensure that these materials, including their own memory, survive beyond their lives.

There are parts in the film where you get the sense that it is more urgent because in Singapore, there is so much that is churning, changing - of our physical surroundings as well as of our memory and views on history.

There are many, and the film touches on a few of the more obvious examples, like parts of the Japanese occupation of Singapore and the experiences of some Chinese-educated student activists in the 1950s, who feel their contributions haven't been accounted for in official history.

Invisible City aims to give you a visceral experience of the atrophy of memories, whether through self-censorship, death or decay of artefacts. And it allows the viewers to muse on how their experience of the present is shaped as much by luck as it is by the efforts of a few preservationists.

Different topics require different treatments. Maybe my next docu- mentary will be more strident.

In everything I've done so far, I have never gone out to court politics. It is partly to do with my personality. I myself prefer to be persuaded rather than being told if something is right or wrong.

Having said that, I've seen polemical movies that are very, very effective. Staying clear of politics here is also a question of survival for me. I don't want to be banned...I want to make movies for the rest of my life here in Singapore.

I don't think a film can radically change the way people think about political issues. Film-makers have been ascribed far more influence than we really have.

In the end, our job is to tell a story. And for documentary directors, it is also to keep a record of the present for the future, which is what Invisible City strives to do.

But even if we wanted to raise awareness in Singapore, it may be difficult to do. For example, the documentary on (former political detainee) Said Zahari, which I think is essential viewing for all students of modern Singapore history, was banned.

There is also the Films Act, which disallows 'party political' films. But the rule is broad and you don't really know what the limits are.