Art historians employ a number of ways to group world arts into systems of classification. They subdivide the continuous flow of artworks through time and space into groupings. These groupings are defined by the perception that the artworks within them share a single quality or a set of qualities that are significant. Significant qualities reflect a specific approach of an artist; they can include the formal, stylistic, iconographic, thematic, or other aspects of art. The definition of a grouping reflects judgments about the nature of meaningful connections between artworks, and between art and its larger context. Western arts are usually structured by art movements, using mostly cultural and aesthetic criteria, while Eastern arts are subdivided into periods according to political-dynastic markers.