Making Gantt charts

One form of very widely-used visualization of time-based data is a Gantt chart. Named after the mechanical engineer Henry Gantt who invented it in 1910s, it is almost exclusively used to visualize work breakdown structures in project management. This chart is loved by managers for its descriptive value and not so loved by employees, especially when the project deadline is near.

Because it is very common, almost every one can understand and read it, even if it is overloaded with additional (related and unrelated) information.

A basic Gantt chart has a time series on the x axis, and a set of labels that represent tasks or subtasks on the y axis. Task duration is usually visualized either as a line or as a bar chart, extending from the start to end time of a given task.

If subtasks are present, one or many subtasks have a parent task, in which the case total time of a task is aggregated from subtasks in such a way that overlapping and gap time is accounted for. This is useful...