(1) Timelines are conventional representations, meaning that they have a familiar structure which the viewer expects.
(2) Breaking those conventions means a viewer must take extra time to figure out what is being shown. If the design is very unusual then it might strike the viewer as completely confusing and they will lose interest, ignore it, or walk away.
(3) The purpose of a timeline is to convey specific information to the viewer that supports your argument, not a “meta” conversation about your artistry or lack thereof. If you make a poster presentation and compliments about your design are the major remarks you receive then you have failed.
• The obvious design is a line — that starts at the left and proceeds to the right, the standard direction of time.
• An arrow can be added to emphasize direction.
• Generally units of time should be proportionately distributed across the timeline. Very large breaks of time can be represented by a dashed line in the timeline and a label explaining it, but it's rarely used. Otherwise, units of time disproportionately represented should be easily understood by the viewer (“Oh, these units of time are not proportionately represented.”)
• At a glance, the viewer should be able to scan and rescan the timeline and understand in a few seconds what it is (“I am looking at a timeline”) and its purpose (“I am being shown this timeline because —”).
Example 1: Conventional timeline
Example 2: Two timelines comparing and contrasting national and local data
Example 3: Unconventional timeline
Example 1: Conventional timeline
Example 2: Two timelines comparing and contrasting national and local data
Example 3: Unconventional timeline
