Coherence across an interface.
WHAT CONSISTENCY MEANS
The same thing looks and behaves the same way everywhere.
WHY IT MATTERS
People learn an interface once, rather than repeatedly.
WHAT TO KEEP CONSISTENT
Spacing Type sizes and weights Colours and their meanings Component appearance Interaction behaviour Terminology
WHAT PRODUCES INCONSISTENCY
Decisions made afresh each time Several people working without shared definitions Additions made under time pressure
WHAT PREVENTS IT
Defined values, documented and reused.
WHAT TO DOCUMENT
The scales, the palette, the components, and when to use each.
WHAT TO REVIEW
New work against the definitions.
WHAT TO DO ABOUT DELIBERATE EXCEPTIONS
Make them deliberate, and record why.
WHAT TO AVOID
Consistency for its own sake, where a case genuinely differs Inconsistency that is merely carelessness
WHAT TO AUDIT PERIODICALLY
How many distinct sizes, colours and button styles actually exist.
WHAT YOU WILL FIND
Considerably more than intended.
