I know that this will probably involve speculation on your part, but take your best guess. (Or maybe there was a DVD extra about it.)
In the film 21, we see a panoramic shot of the Boston skyline, with the Mass Ave bridge in the foreground. The camera looks like it’s several hundred feet away (to the west), and at least a hundred feet high. A man is riding a bike north along the bridge.
The camera pans over the bridge to the east, circles around the man, and zooms in to his face and torso, then paces him as he rides.
They couldn’t have used a helicopter, as they couldn’t have zoomed in that close, right?
If this was CGI, I’m going to be really disappointed.
I haven’t seen the film, so I can’t say for certain. I’ll bet, though, that they built the scene up from components filmed in different fashions, then blended together with the help of a computer and some CGI. That, I understand, is how they did that incredible opening shot for The Birdcage, with the camera coming in over the water, then up the beach, then across the street, then in through the doors of the club, through the crowd, and onto the stage. You couldn’t do that all with a hand-held, or with a helicopter.
Ooh, Ooh, I know this one! I’m a commentary geek and so heard how they did it, and it was in a featurette.
Helicopter shot until it got close to the bridge, and then a moving crane shot. The transition was when a bus went by - that was a CGI. Well done, and made me say “how’d they do that?” too, when I first saw it.
I think the director was pretty proud of it, too, since it was a featurette, and he had to mention it during the commentary. Good movie.