How does E. L. Doctorow use imagery in Ragtime?

Imagery:

Everyone wore white in summer. Tennis racquets were hefty and the racquet faces elliptical.

Riis made color maps of Manhattan’s ethnic populations. Dull gray was for Jews—their favorite color he said. Blue for the thrifty German. Black for the African. Green for the Irishman. And yellow for the cat-clean Chinamen… Add dashes of color for the Finns, Arabs, Greeks and so on, and you have a crazy quilt, Riis cried, a crazy quilt of humanity!