101 Dalmatians|Trafalgar Square — Where One Leash Decided Two Lives

The chase starts here, and it starts badly for Roger Dearly. Pongo has caught sight of Perdy across the paving, and the man on the other end of the leash discovers he has no say in the matter. They come along the north side of the square, past the fountains, under the column, with a designer on a bicycle somewhere ahead and gaining distance.

Watch the sequence now and you notice something the film never meant to preserve. In 1996 there was still a road along the north terrace, running directly beneath the steps of the National Gallery, and traffic moving through the frame. That carriageway was closed in 2003 and the terrace became the broad flight of steps and open plaza people sit on today. The stone is the same, the lions are the same, the geography of the joke survives — but the specific danger of a loose dog crossing that side of the square has been engineered out of existence.

Come early, before the tour groups mass at the base of Nelson's Column. Stand at the top of the north steps and look south-west, toward Admiralty Arch and the opening of The Mall. That is the line Pongo took, and it is the only direction the rest of the film could have gone.