Law of Continuity
We tend to follow smooth lines and aligned elements as one path.
Alignment gives the eye a route to follow.
A checkout tracker connects four steps with one line. Your eye follows the route from basket to confirmation. Move one step away from the line and it no longer feels like part of the same sequence, even if its label is correct.
Origin
Wertheimer described the factor of direction, now often called good continuation, in 1923. His examples showed how line segments group as a smooth path instead of separate pieces. The principle remains part of modern perceptual research.
Align related content to a shared edge. A clean column is easier to scan because the eye does not need to find a new starting point on every row.
Connect steps when order matters. A line through a progress tracker or timeline turns separate labels into one route.
Break alignment only when the separation is meaningful. A small accidental offset can make an item look detached from its group.
Recheck paths on narrow screens. Wrapping, stacking, or clipping can interrupt a line that worked well on desktop.
Digital systems
A Progress Tracker
A line connecting checkout steps helps them read as one sequence. Highlighting the completed part shows how far the person has moved along that path.
Physical signals
A Subway Map
A colored line connects the stations on one route. Riders can trace that line across the map and notice where it meets another route without treating each station as an isolated point.
When related items do not share an edge or path, the sequence becomes harder to follow. People must work out the order from labels that the layout could have shown directly.
Align related elements and connect ordered steps. Keep the path intact as the layout changes, and use a deliberate break only when you want to show a real change in relationship.