What concept involves sizing design elements in relation to their relative importance and to each other?

The concept that involves sizing design elements in relation to their relative importance and to each other is hierarchy. Hierarchy in design is about creating a sense of order and structure, which helps viewers understand the relationship between different elements. It establishes a visual organization that guides the viewer's attention, emphasizing the most important elements and de-emphasizing others.

By using size, color, contrast, and placement, designers can indicate which elements are primary and which are secondary, thereby leading the viewer's experience through the content in a meaningful way. This organization is crucial for effective communication in design, making hierarchy a foundational principle in both graphic and web design contexts.

In contrast, balance refers to the distribution of visual weight in a design to ensure stability, while proportion deals with the size of elements in relation to their overall dimensions and the space they occupy. Alignment concerns the positioning of elements in relation to each other, ensuring a cohesive layout. Each of these concepts contributes to the overall design but does not specifically address the sizing in relation to importance as hierarchy does.