In graphic design for posters, the principle of "matching shape" is key to visual harmony. It requires that all design components—images, text boxes, and background frames—exhibit consistent shapes and contours. For example, posters with rounded images should feature text boxes and other elements with similar rounded edges to maintain aesthetic consistency and professionalism.

This technique prevents visual discordance, such as mismatched corner radii, which can disrupt the design's flow. Instead, uniform shaping unifies the composition, resulting in a cleaner, more cohesive look. By maintaining a consistent theme, this approach also enhances readability and viewer engagement, making the design more effective and appealing.