Symbolism, Imagery, Allegory
Bombay, or Mumbai, is a city made up of several islands. The ever-present sea is an important part of the novel's theme of exile, reminding Lin and his pals of their homes across the ocean, and the way that they are trapped.
Lin loves to go sit at the beach when he's feeling lonely. At one point he even gets explicit about the meaning of the island for the exile: "All of us were refugees, survivors, pitched up on the shores of the island city" (2.16.129). The idea of being washed up onto Bombay's shores rather than deciding to go there deliberately highlights the chaos of exile life.