Make an Overlapping Timeline
An overlapping timeline shows events that happened at the same time, each drawn as a bar from its start date to its end date. Where two bars cover the same stretch of the date axis, the events overlapped, and the length of that shared stretch shows by how much. A list of dates can tell you that two things happened in the same decade. An overlapping timeline shows that one began three years into the other and outlasted it.
They are useful wherever periods run side by side: reigns and wars in a history class, jobs and studies on a career timeline, the lifespans of relatives in a family history, or the phases of a project that start before the last one finishes.
1. Give every period an end date
An overlap needs two bars, and a bar needs both dates. When you add an event, fill in the End Date as well as the Start Date. If you know how long something lasted rather than when it ended, type a duration such as 3 years or 9 months in the End Date field and Preceden works out the date. For something that is still going on, type Present.
An event with only a start date is drawn as an icon instead of a bar. That suits a one-day moment, such as a signing or a battle, but an icon cannot show how much it overlaps with anything.
2. Check the dates where two events meet
Preceden counts the end date as part of the event (see What Inclusive Dates Mean). A job that ends in June 2020 and another that starts in June 2020 both cover June, so they overlap by a month on the timeline. If the first one really ended before the second began, end it in May, or use exact dates such as June 12 and June 15.
How Preceden places overlapping events
Within a layer, Preceden lays events out in order of their start dates. By default each event gets its own row, one below the other. Overlaps are easy to read that way, but a timeline with many events gets tall.
To make it more compact, click Appearance, open Layers, and check Automatically compress layers. Preceden then moves each event up to the highest row where it fits without running into another event. Events that never overlap share a row, and events that run at the same time stack above and below each other.
Preceden checks each event's name and details as well as its bar, so a name placed to the right of one bar can keep the next event off that row. Under Appearance > Events, setting Bar Content Layout to Name and details inside keeps names and dates inside the bars, which lets bars share a row whenever their dates don't overlap. Bar Content Layout Settings compares the options.
If you would rather arrange the rows yourself, leave compression off and drag events up or down to the row you want.
Group overlapping events with layers
When the overlaps you care about are between groups, such as two countries, two people or several teams, put each group on its own layer. Layers sit one above another on the same date axis, so a bar in one layer lines up with whatever was happening in the others at the same time. Give each layer its own color with the Color field, then click Appearance, open Colors, and check Override event color with the layer color so each group is easy to pick out.
Make a Comparative Timeline covers layers for different subjects, and Make a Swimlane Timeline covers layers for different teams in a plan.
When every event needs its own row
If you are planning tasks and want each one on its own row with its name down the left, check Use Gantt chart layout under Appearance > Layers. A Gantt chart always gives each event its own row, so overlapping tasks never share one, and the compress setting is hidden while the layout is on. See Creating Gantt Charts with Preceden.