The interpretations of drawings is closely related to those in handwriting analysis. Many of the same principles are used -- the way the page is filled, level of detail, types of strokes, proportions, accuracy and much more. From all of this it is possible to provide a personality profile.
Drawings can reveal feelings, influences and interests -- the artist's inner emotional state and development. When used in conjunction with handwriting analysis it can either confirm a personality profile, or reveal traits not evident in the handwriting. Analysis of a person's drawings is also a common practice used in child psychology. Tests like the House-Person-Tree test or the Draw a Person test help the psychologist gain an understanding of the child's mental and emotional state.
Asking a subject to draw a picture also presents a maximum of ambiguity for the subject. Whereas tests that present a stimulus card which does not change over time, having the subject create a picture presents the subject with a completely blank field onto which they are asked to draw and project. Every subject will draw a tree, but every tree will differ. The result is a collection of projective material organized around standard themes and freedom from stimulus bias.