Why is New York City called the Big Apple?
According to the Museum of the City of New York, the phrase "big apple" was first used by Martin Wayfarer to describe New York City in 1909. He used it in a metaphor describing how New York, "the big apple," gets a disproportionate share of the sap from the country's tree of wealth which is rooted in the Mississippi Valley.
The saying evolved in the 1920s when New York Morning Telegraph sports writer John J. FitzGerald overheard African American stable workers using the phrase while talking about New York's racing scene, which was considered "the big time." Fitzgerald liked it so much he named his racing column "Around the Big Apple." Jazz musicians in the 1930s and 40s made it more popular by using it in the same way, referring to the New York jazz scene as "the big time."
The name became less prominent for the next two decades until the New York Convention and Visitors Bureau used a red apple during its campaign to increase tourism in the 1970s. Since then the apple has become an international symbol for New York City and the phrase, its unofficial nickname.
—The Fact Monster