A good example of how Chekhov builds isolation through imagery in "The Lady with the Pet Dog" is found in the very beginning of the story where he uses imagery of isolation to set both the tone and mood (i.e., atmosphere) of the story. First of all, the reader is told "It was said." Ivan didn't say to Anna. Petrovich didn't say to Andreovich. It was said. Immediately, Chekhov has created a image of distance and anonymous people who talk at some unspecified place and some unidentified time in some indefinite conversation where it was said that a new person had arrived at Yalta.
The new person is then seen from a remote distance "walking on the sea-front," thus establishing a buffer of unapproachability and isolation around this new arrival, a buffer that works both ways as no one approaches her and she approaches no one across the expanse of the sea-front. Even the Pomeranian dog "running behind her" confirms the distance and isolation; had the dog run with her or beside her, Chekhov would have created the possibility and expectation of approachability and the story would have been a different story.
That the new arrival always is seen in gardens--where people are kept at a distance by rows of flowers or bushes in flower beds and by hedges building foliage walls--or in open public squares--where numbers of people are spread about without connection between them--builds another layer of distance and isolation around the characters. Even Gurov's interactions with other people embeds the theme of isolation within the text. With men he is distanced and bored. With his wife he is frightened, having no desire to be in his home, which in someways describes the ultimate isolation: his home is where he desires isolation and distance.