A reference line is typically used to mark a specific value or region on an axis. For example, if you are analyzing the monthly sales for several products, you may want to include a reference line at the average sales mark so you can see how each product performed against the average. Alternatively you may want to shade a particular area along the axis. Finally, you may want to use reference lines to specify a distribution. There are three types of reference lines: lines, bands, and distribution.
Tableau lets you add an unlimited number of reference lines. Add reference lines using the Add Reference Line dialog box.
Types of Reference Lines and Bands
Adding Reference Lines
You can add a reference line to any continuous axis.
Adding Reference Bands
Reference bands are shaded areas behind the marks in the view between two constant or computed values on the axis
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Adding Reference Distributions (Bullet Graphs)
Reference distributions are a variation of reference bands. A reference distribution adds a gradient of shading to indicate the distribution of values along the axis. Distributions can be defined by confidence interval, percentages, percentiles, quantiles, or standard deviation. In addition to the shading, you can add a line to mark a constant or computed value along the axis.
Example: To add a reference line:
Right-click on a quantitative axis and select Add Reference Line.
In the Add Reference Line dialog box, select Line.
In the Add Reference Line dialog box, select one of the following scopes:
Select the Value to mark on the axis. You can select from the following options:
- Average – places a line at the average value along the axis.
- Constant– places a line at the specified value on the axis.
- Maximum – places a line at the maximum value.
- Median– places a line at the median value.
- Minimum – places a line at the minimum value.
- Sum – places a line at the SUM of all the values in either the cell, pane, or entire view.
- Total – places a line at the aggregate of all the values in either the cell, pane, or the entire view. This option is particularly useful when computing a weighted average rather than an average of averages. It is also useful when woring with a calculation with a custom aggregation. The total is computed using the underlying data and behaves the same as selecting one of the totals option the Analysis menu.
These values can be applied to any of the measures used in the view. For example, in a view showing sales over time, you can add a reference
line that marks the average profit. If there are multiple measures in the view, select the measure to use to compute the reference line.
Select how you want to label the line. You can select from the following options:
- None –select this option to not include a label for the reference line.
- Value – select this option to include a label that is the corresponding value on the axis.
- Computation – select this option to display an automatic label. The label is based on the computation and the measure that is selected.
- Custom – select this option to type a custom label into the text box. You can use the menu to the right of the text box to insert values such as the computation or the value.
Specify Formatting options for the line. You can change the style, thickness, and color.
Optionally, add a Fill color Above and Below the line.
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