Law of Common Region
Elements tend to be perceived into groups if they are sharing an area with a clearly defined boundary.
Structure and relationship
Common region creates a clear structure and helps users quickly and effectively understand the relationship between elements and sections.
Borders
Adding a border around an element or group of elements is an easy way to create common region.
Backgrounds
Common region can also be created by defining a background behind an element or group of elements.
Origin
Gestalt psychologists Max Wertheimer, Kurt Koffka and Wolfgang Kohler developed a set of principles in the early 20th century aimed at describing how people naturally perceive objects as organized patterns and objects. These principles, commonly referred to as Gestalt laws principles, are organized into five categories: proximity, similarity, continuity, closure, and connectedness.