Wersba deftly weaves a contemporary setting into the fabric of plot and theme. Fat is set on Long Island, New York, in a town called Sag Harbor (where Wersba herself lives). It is a small town deluged by tourists in the summer and deserted the remainder of the year. Rita laments the crowded highways, grocery stores, and beaches during tourist season in Sag Harbor, calling summer "an interlude that we locals have to grit our teeth to endure."

Wersba provides ample description of Rita's adventures in shops, a health club, the mansion district, and the countryside.

The setting of the book complicates Rita's love for Robert Swann by illustrating the division of economic classes. Rita finds the rich "very annoying": "Every summer they swarm out to Long Island, where they crowd the beaches and where their kids get busted for drunk driving, and then they depart—leaving...