Studies of design creativity have underlined the importance of divergent reasoning and visual reasoning in idea generation. Connecting these two key design skills, this paper presents a model of divergent visual reasoning for the study of creativity. A visual divergence task called ShapeStorm is demonstrated for the study of creative ideation that can be applied to humans as well as computational systems. The model is examined in a study with human subjects, a computational stochastic generator, and a geometrical analysis of the solution space. The main significance of this task is that it offers a straightforward means to define a simple design task that can be used across research studies. Several scenarios for the application of ShapeStorm for the study of creativity are advanced.