How does the author use metaphor in the novel, Unhooking the Moon?

The Rat refers to New York City as the “Emerald City” a metaphor for escapism and promise. Her dream was to find her protector who lived among tall buildings – an obvious reference to the skyscrapers of New York City. “Unhooking the Moon”, the title of the book, stands for just how far Bob would go to keep his sister safe and close to him – he would unhook the moon for her.