Levi Asher has an interesting piece of literary detective work here on Literary Kicks. Using an online historical mashup map which shows New York City in 1924, he tracked down what he believes to be the location of the 'Valley of Ashes' in The Great Gatsby. Click here for our own ShowMe analysis of Nick Carraway's description of this desolate location.
After spending many hours studying the map and carefully determining the exact coordinates represented in Fitzgerald's novel, I walked by the exact spots described in the passages above. I saw a small auto repair shop. I saw a couple of rundown coffee and fried-egg breakfast/lunch cafes, where the people who work in the nearby factory take their breaks. The main factory makes signs -- large mounted billboards, specialty plastic displays. It looked like this business had been there a long time, and I now believe (though I have not yet verified this, and am not sure exactly how to do so), that if F. Scott Fitzgerald had ever seen an actual sign for an eye doctor at this spot, it might not have been because the eye doctor was located nearby. Rather, the sign-maker might have been constructing the sign, or may have been displaying it to advertise his work.