Similarity with shape
Similar elements are immediately perceived as related by users. Elements that share the same shape, color, size, or other properties are viewed as a group. It’s one of the main reasons designers stick to one button shape throughout a design or use all black and white images of the same size and shape. The same-shaped images in this example demonstrate they belong to a single group.
Pro Tip: Be careful not to use the same shape for elements that are not related, as it can make users perceive them as a group.
