Artworks or series of artworks illustrating a classification system or set of types. Two of the best known examples are August Sander's "People of the Twentieth Century" (c. 1927-1964) and Bernd and Hilla Becher's "typologies" (1960s onward). Sander's series presented a selection of types of people—such as farmers, factory workers, socialists, and actors—in the desire to create a complete cross-section of German society. The Becher's "typologies" are most often grids of black-and-white photographs in which each picture in the grid is a different example of a type of industrial building or structure, such as water towers, blast furnaces, or gas tanks.