Each of these locations means something slighty different to Gatsby, Daisy, Nick, Tom, etc., but there are some commonalities. New York is for Tom a place to play and misbehave with his mistress Myrtle. For Myrtle, New York is escape from her horrible life with her husband (in the "valley of ashes"). New York for Nick is a place of a different kind of opportunity -- success in business. It is, for most characters, an "other" place. A place outside of most of the action of the story, it is a place that's an escape from the oppressive atmosphere of Long Island. The "valley of ashes" represents the real world of most of the people of the United States. It is a blighted, poor area in which Myrtle and her husband live. It is ugly and depressing, and is in contrast to the bright lights of the city and the protected beauty of West and East Egg. It is quite literally a place of death (Myrtle's), rather than one of life or hope. West and East Egg represent where the best of society should be at peace. Tom and Daisy are in the very best section (East Egg), while the parvenu Gatsby and the relatively poor Nick are left to gaze with longing across the water at East Egg from the less-fashionable West Egg. East Egg represents, at least for Gatsby, a kind of unattainable heaven (containing Daisy). West Egg was supposed to be a refuge from the city's heat for Nick, but as the events of the summer unfold it becomes a place of sadness and lost hopes.
Nick is middle class