As a pastime, watercolor legend Edgar Whitney inventoried and cataloged successful painting compositions. He weighed the primary visual masses by size and value as well as arrangement and came up with six visual themes that most successful paintings appear to fall into. As an aid for composing paintings, these themes were passed on to his students, including Tony Couch, who wrote about them in his book: Watecolor: You Can Do It!
What we have here are the symbols of first impressions of paintings. The vague shapes and values that first attract your eyes to interesting paintings have no subject matter. Here I've represented the six compositional themes geometrically, but the hundreds of paintings Mr. Whitney analyzed to get these compositional hints covered diverse subject matter and genres.
These are the themes, the arrangements of masses and shapes, that are popular attention getters for artists. They can be applied to plein air painting as well as figure painting. Take them into consideration for possible inspiration when you pick up a pencil, brush, stylus, or mouse.