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.