Continuity is a gestalt concept that refers to the visual tendency to create continuous figures. Continuity is most commonly (though not exclusively) exhibited in the perception of lines and refers to the tendency to “carry the line forward.” More specifically, there is the tendency to continue smooth figures forward over abrupt changes in direction.

Below, continuity describes the tendency to see the left figure as two curved lines. The right figure depicts how the two curved lines are generally seen, one red and one blue.

While the red/blue illustration is the likely perception in the previous example, continuity describes a tendency for smooth figures over abrupt changes in direction. The example below is another perception of the same two blue lines and exhibits abrupt changes in direction at the intersection of the two lines. This is an unlikely interpretation of the two blue lines and does not exhibit good continuity.

Continuity also describes grouping. The figure below is generally perceived as a line rather than individual circles.

Good continuity is exhibited across the line of heads.
Limbourg brothers. Pentecost.

Good continuity is exhibited between the horizontal and vertical elements.