Spark Lines refers to a visualization that uses multiple small line graphs that are designed to be read and compared quickly. The goal of Spark Lines is to give a visualization that can be understood at a glance. You aren't trying to communicate exact values, but rather give the audience the ability to quickly understand trends, movements, and patterns.
Among various uses of this type of visualization, you may have seen Spark Lines used in financial publications to compare movement of stock prices. Recall, that in Chapter 1, Taking Off with Tableau, we considered the initial start of a Spark Lines visualization as we looked at iterations of line charts. Here is a far more developed example:
This chart was built using the following features and techniques:
- Start with a simple view of the Sum(Sales) by Quarter of Order Date (as a date value) with Category on Rows.
- Two calculated fields have been created to show the minimum and maximum quarterly sales values for each category. Min Sales has the code WINDOW_MIN(SUM(Sales)) and Max Sales has the code WINDOW_MAX(SUM(Sales)). Both have been added to Rows as discrete (blue) fields.
- The calculation Last Sales with the code IF LAST() == 0 THEN SUM([Sales]) END has been placed on Rows and uses a synchronized dual axis with a circle mark type to emphasize the final value of sales for each timeline.
- The axis for SUM(Sales) been edited to have Independent axis ranges for each row or column and the axes have been hidden. This allows the line movement to be emphasized. Remember: the goal is not to show the exact values, but to allow your audience to see the patterns and movement.
- Grid lines have been hidden for Rows.
- The view has been resized (horizontally compressed and set to Fit Height). This allows the Spark Lines to fit into a small space, facilitating quick understanding of patterns and movement.