From a long article by Charles McGrath on Edith Wharton's New York (from the New York Times; free registration required):

On Wharton's map, civilization ends north of Central Park, except for satellites in Newport, Rhinebeck and Tuxedo Park. Her New York is very slender — it stretches from Third Avenue to Sixth, essentially — and its center is what is now the campus of New York University. If Steinberg had drawn Wharton's New York, he would have shown it from the point of view of someone looking through the Washington Square Arch.

. . . . .

Besides the north-south axis, the other great demarcation in Wharton's New York is the one dividing east from west. The East Side is where the fashionable young people live, like Lawrence Selden from "The House of Mirth," who has rooms at the Benedick, at 50th and Madison, or Newland and May Archer, who after their wedding settle in a brand-new house on East 39th, a neighborhood both remote and a little experimental, where the younger architects are beginning to use "ghastly greenish yellow stone . . . as a protest against the brownstone of which the uniform hue coated New York like a cold chocolate sauce."

The West Side is where the vulgar hotels are; it's also where the poor and the oddballs live, like the inhabitants of the strange little neighborhood on West 23rd where Madame Olenska briefly resides in "The Age of Innocence": "small dressmakers, bird-stuffers and `people who wrote.' " The farther west you go, apparently, the more things run down; Lily Bart's downfall is so complete that she winds up living in a boarding house so many blocks west of Sixth that the railings are no longer painted and garbage is carelessly strewn around.

Not a lot of real work gets done in Wharton's New York — except by the seamstresses in the workroom at Madame Regina's renowned millinery establishment, where Lily briefly finds employment. Some of the younger men, like Newland Archer, dabble at legal careers, but not so seriously that they can't take months off to go to Europe or to Newport. This is a world that is financed for the most part by inherited wealth, and where people from the middle and working classes are seldom glimpsed. Even the servants are invisible, and so is the bustle of immigrant life that so impressed Wharton's contemporary William Dean Howell[s].