Sister Carrie is a naturalistic novel that places a naive, innocent young woman in the city of Chicago with its grime, crime, exploitation, and urban corruption of soul.  Carrie is unprepared for the events in her life and is victimized by her environment, one too harsh for her naivete.  Only two generations removed from the emigrant, Carrie is

[I]n the intuitive graces still crude. She could scarcely toss her head gracefully. Her hands were almost ineffectual....A half-equipped little knight she was, venturing to reconnoiter the mysterious city, and dreaming wild dreams of some vague, far-off supremacy....(Ch.I)

But life is Darwinian for Carrie and the ingenuous Carrie does not fare well in the cold, harsh city and "[S] felt the drag of a mean and narrow life."  The city is a hostile environment in which a defenseless young and naive woman does not fare well. Later in the novel when she becomes a mistress,

...her name is bandied about in the most frivolous and gay of places, and that also when the little toiler was bemoaning her narrow lot, which was almost inseparable from the early stages of this, her unfolding fate. (Ch. V)

Another aspect of cities is the economic one. Some critics interpret Carrie as a capitalist. Since it is economic forces that allow a person to rise or fall in the setting of this novel, Carrie’s problem becomes one of economics. And, sadly, she soon learns that the greatest thing that she has in exchange for money and goods is herself.  So, sex becomes her capital in this city in which only the strong survive.

A city novel perfectly captures the time and place in which it is set.  Sister Carrie captures the city of Chicago in the late 19th century.  This was a tumultuous time for the city, one full of corruption and moral decay.  Sister Carrie presents us a picture of this time.  We see a city experiencing growing pains.  

The city has its cunning wiles, no less than the infinitely smaller and more human tempter. There are large forces which allure with all the soul fullness of expression possible in the most cultured human. (ch 1)