Chapter 11


Providing an understanding how values change over time is one of the most fundamental functions of visualization, and the presentation of this type of information has evolved significantly since it was invented. Timeline visualizations serve as an aid to comprehension, allowing you to extrapolate and predict a trend. For example, if sales are consistently increasing by $100,000 per month over the last three months, it is easy for the human eye to imagine an increase over the upcoming months. Similarly, seasonality, such as the sales increases in the retail sector for the Christmas shopping season, becomes easy to see as a chart line rises and falls. Trends can be built into the charts as well as trendlines. Care must be taken when using trendlines to ensure that the user of the chart is kept aware of the fact that trends are derivations based on the data rather than actual measured values. Statistical predictions are another way of creating trendlines.

Historical Use of Temporal Analysis
The earliest examples of timeline visualizations were in the mid-17th century, when Joseph Priestly created a timeline to compare the lifespan of various people, as illustrated in the “Timelines” section later in this chapter, and the convention of time being shown as running left to right, used to match the direction in which the names on the timeline have been read is one that we continue to use for visualizations. William Playfair, who you read about in Chapter 2, extended ...

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