Which Gestalt grouping principle explains why the nine dots to the left look like three columns of three dots each?

Question

Quizplus · Accepted Answer

The principle of proximity states that objects that are close to each other tend to be perceived as a group. In this case, the dots are arranged in such a way that they are closer to the dots next to them than to the dots farther away, leading us to perceive them as three columns of three dots each.

Which Gestalt Grouping Principle Explains Why the Nine Dots to the Left