A sparkline is a graphic used to convey information in a text. By definition, sparklines take up very little space but convey a lot of information. They are usually used to map change over time. A common use for sparklines is to graph stock activity or economic fluctuations.
The term sparkline was first used by Edward Tufte, an American statistician and professor at Yale University. Tufte wrote a series of books on displaying information using graphics. His theory of sparklines is outlined in the book Beautiful Evidence, which was published in 2006 by Graphics Press.
Sparklines can take many forms. The most commonly seen sparkline has three basic elements. A line graph shows change over time. A title, between one and three words long, tells what the graph measures. Finally, a number shows the total or final result of the graphed changes. More elements can be added, but the object of a sparkline is to keep the graphic as simple as possible while still conveying the necessary information.
A sparkline is usually embedded in the text of a book or document. The graph and its accompanying information appear in line with the text. They are usually about the same height as the text line on which they are placed. Information shown in a sparkline illustrates the text that appears directly before or after it. This allows the reader to view the graphic without interrupting his or her reading.
For example, in an economics text, if the author wanted to show how the Dow Jones industrial average has changed over time, he or she could use a traditional graph with an x-axis labeled time and a y-axis labeled points. The author could then insert a line note telling the reader to see figure 1-A. Then the reader could stop reading, find figure 1-A, and review the graph. Tufte thought that instead of distracting the reader’s attention this way, it was best to simply insert the graphic directly into the text.
Tufte also put forth the concept for something called a small multiple, a graphic that includes several sparklines. Each sparkline graph has its own x-y axis so that each piece of information is self-contained. Yet the sparklines are close enough together to be viewed simultaneously. This allows for comparison without visual confusion. Small multiples are most useful for comparing things that change over time but are not measured using the same scale.