the original writer creates an impression that he is describing two cities
Exactly! You have caught, felt his intention. He is making the stark contrast in words, what the film-maker did in images: a Paris he remembers and knows, with those distinctive features and ways of life that are quintessentially the life of Paris and which survive and endure, and a Paris that is dying, to exist only as a dream remembered, a ghost. Paris is lovers walking under the bridges of the Seine. Paris is the artists of Montmartre. Let one disappear, and a 'Paris' disappears.