LOS ANGELES–The creation of a movie about the only man to survive a virus that kills millions, including the entire population of New York City, would be difficult enough if you were shooting it in a studio and using a green screen to create the look of a city in ruins. That degree of difficulty would increase greatly if you decided to shoot it on location in Manhattan. And if it was only your second film, the odds against it being fun would probably be too high to bother calculating.

Director Francis Lawrence, who came to the making of I Am Legend on the back of the movie Constantine and dozens of commercials and videos, says that although it wasn't the easiest of shoots, he had a surprisingly good time.

"The really hard part was that we could only shoot in Manhattan on weekends," he says in an L.A. hotel room. "We were chasing the seasons. We would say, 'If we get rained out until next weekend, that will push next weekend's work up even more.' So it was a real race to get all the exterior work done before the leaves were gone. But nothing was simple. You had to wait for the traffic to go through and for the people to be pushed back behind buildings. Occasionally there were problems because you couldn't just hold people back if they were marching through the shot. I mean, everyone's supposed to be dead except Will [Smith]'s character, so it was tough when they wouldn't leave. But for the most part they were good."

In I Am Legend, which opens next Friday (December 14), Smith plays Neville, a virologist who is the last man in New York City and who may be the only true human left on the planet. There is just him, his dog, and the walking dead who come out at night, intending to kill him if they can find him. Neville believes he may be able to find a cure and revert them to human form.

Lawrence says that few people recommended that he shoot in the streets of New York City, but that he, writer Akiva Goldsman, and Smith felt that it was the only way to make the film look real: "I think that when you shoot against green screen all the time, it starts to look a little fake. It [location filming] also informed the actors in a different way. When they were out in the weather and in the elements and on a real street and there was no one else and no cars going by, it added an air of naturalism.

"Even though we emptied everything out, we still had to worry there were signs of life in the distance and lights on in buildings and steam coming out of places and traffic lights, all of which had to be taken out in editing. But having real light and real particles in the air just added realism and, I think, makes it more frightening."