Notan is a method of thinking about and then drawing a composition. It helps the artist analyze a composition with the goal of making changes to improve it. It is one way of making a value study.
Numerous sources indicated that the word notan comes from Japanese but different sources present differing ideas on the origin of this concept. Most sources do agree that the word relates to dark / light or full / empty. Perhaps the most easily recognized example of notan is the Chinese yin and yang symbol. It shows a balance of dark and light with one within the other.
Notan aids an artist when designing a composition because most often when a composition is simplified into black and white and the resulting shapes combine to form a pleasing arrangement, this leads to success for a drawing or painting. So when making small drawings of your composition ideas (often called thumbnails) simplify them to two values and see if the resulting shapes are pleasing. If not, make adjustsment in the shapes until you find an engaging balance. But to be clear, a strong notan design does not need to be 50% black and 50% white. Most often successful notan designs are not 50/50. Often they are 35/65, 40/60, of even 30/70. Consider how the shapes in the yin yang fit into each other like puzzle pieces.
As you make compositional studies for your paintings, try simplify your design into notan drawings. I expect you will find the end results to be helpful.
Claude Monet, a famous French Impressionist, is known for his beautiful colors, but notice that the foundation of this painting, the value plan, is engaging all by itself. The black and white silhouette of the building is visually pleasing even without the color.
Here are some notan studies that I made of paintings that I think are strong.