In the Great Gatsby, there are two cities, East Egg and West Egg, which are separated by the Valley of Ashes. What city you live in between the two, shows if you are from a wealthy family (East Egg) or if you are new to wealth (West Egg).
People in East Egg come from families that always had money. They're more snobby, greedy, and mean than people from West Egg, as those from East Egg are generally less-sophisticated, and a more innocent type of people, as they haven't been consumed by material possessions, money, and greed their whole lives. The Buchanans, for example, are a family of East Egg, which Tom Buchanan was born of a wealthy family, and the greedy Daisy, who married into this money. They have a very large mansion for a home, and are a somewhat of a stuck up family. East Egg is portrayed as corrupt in the novel, and and is moral-less, compared to the more humble West Egg.
According to F. Scott Fitzgerald, the West Egg is "less fashionable" with "wide lawns and friendly trees." Most of the people that live in the West Egg have morals and ethics to live by, rather than their own money, such as Nick Carraway. After Nick does Gatsby the favor of reuniting him with Daisy, he offers Nick the chance to take part in Gatsby's business and earn more money. Even though Nick struggles to sell bonds, he politely declines, realizing that Gatsby was only returning the favor. This shows that Nick has dignity, and doesn't live off the image portrayed by how much money he has or makes.
Sources: The Great Gatsby