Tennessee Williams understood the deliberate purpose of the setting in A Streetcar Named Desire. Williams's stage directions indicate this importance in describing New Orleans:
...a peculiarly tender blue, almost a turquoise, which invests the scene with a kind of lyricism and gracefully attenuates the atmosphere of decay. […] In this part of New Orleans, you are practically always just around the corner […] from a tinny piano being played with the infatuated fluency of brown fingers. […] New Orleans is a cosmopolitan city where there is a relatively warm and easy intermingling of races.
Such a set of stage directions speaks to how purposeful and meaningful New Orleans is as a setting. New Orleans is the perfect backdrop to the condition that impacts the major characters, such as Blanche. The "lyricism" that "gracefully" reflects the condition of "decay" is intrinsic to Blanche's condition. Blanche arrives to New Orleans in a condition of decay, and almost out of place in a constantly changing world. As the "Blue Piano' expresses the spirit of the life which goes on here," it becomes clear that such a song is one that Blanche does not sing. This is one way in which the setting of New Orleans holds importance in the thematic growth and characterizations within the drama.
I think that the setting of New Orleans and Stanley's apartment is important because it provides a stark contrast to the world of Blanche Du Bois. Belle Reve is never seen in the drama, except through Blanche's eyes. It exists in the past, and more significantly, her past. This "beautiful dream" is a reflection of the world to which Blanche wishes to return. The setting of the Kowalski Apartment and New Orleans are settings that are diametrically opposed to the dream- like condition of Blanche's world. The working class feel of the apartment and the vitality of New Orleans helps to make Blanche even more out of place of the world. This dissonance helps to increase her own decay, and her own condition as "the other." Once again, the use of setting helps to enhance the characterizations and theme of change that is so much a part of the narrative.
Setting becomes an important tool in Williams's hands. He is able to use setting as a way to increase the gulf between Blanche and the world. It is a tool in which themes can be developed as well as characters can be fleshed out and their aspects illuminated. There is no peace in the world of New Orleans and the Kowalski Apartment. Life teeming with life is evident in both worlds, settings in which Blanche is further alienated and set apart from others.
When Blanche says, "Whoever you are, I have always depended on the kindness of strangers," it is a statement that does not apply to the world of New Orleans, the Kowalski apartment, or the modern setting, in general. This statement is able to acquire meaning in understanding Blanche because the setting illuminates her lack of connection to the world and those who inhabit it. This is a way in which setting has significance and importance in the drama.