How does O. Henry undertake a critique of urban space in "The Gift of the Magi"?

O. Henry vaguely describes the simplicity of Jim and Della's city apartment. They live in an urban setting and have very little money. O. Henry moved to New York City in 1902, and he published "The Gift of the Magi" in 1905. He experienced life in a large urban setting firsthand in the years leading up to writing this story.
Those living in poverty in urban settings during the early 1900s often had small, simple apartments like the one in the story. These spaces were typically cramped and often had low levels of cleanliness.
Della and Jim rent a furnished apartment, which they pay $8.00 per week for. The included furnishings are meager, and include a "shabby little couch." O. Henry also describes the cheap glass in the apartment window:

There was a pier-glass between the windows of the room. Perhaps you have seen a pier-glass in an $8 flat. A very thin and very agile person may, by observing his reflection in a rapid sequence of longitudinal strips, obtain a fairly accurate conception of his looks. 

The descriptions of the worn sofa and the mirrors one can scarcely gaze into give the reader a sense of simplicity. This simplicity shows O. Henry's analysis of life in a humble urban apartment.