Proportions and Percentages - Communicating Data with Tableau - page 97

Reference Lines
Tableau has the ability to add a variety of types of reference lines and bands to charts that
can be used to aid comparison. The bullet chart has built-in reference lines, but they can be
added manually to any chart type.
To learn more about them, let's take a closer look at what Tableau added to the bar chart in
Figure 5-14 . Click in the x-axis area of the bullet graph, click Edit Reference Line , and notice
there are two options to choose from. Tableau has created average 2011 HR lines (dark ver-
tical lines in each row) and 60% and 80% bands for the 2011 figures (resulting in the differ-
ent shaded areas in each row).
Figure 5-18 shows the dialog boxes that could be used to create these reference lines in any
chart.
Notice that the dialog box on the left creates a line for every cell (row) that is equal to the av-
erage of the SUM(2011 HR) . Because there is only one 2011 home run value for each team,
the average is just that one value. The dialog box on the right creates distributed banding for
each cell (row) that is equal to 60% and 80% of the 2011 HR average. Again, the average is
just the single 2011 value for each team. The formatting controls the color of the fill, and
how to fill in the regions between the boundaries.