Line Visuals with Dual Axis

It is often enlightening to see related dimensions on the same line chart; it clearly shows both correlation and pattern. However, values may be measuring completely different things, or the range of values (scale) is too different to show both lines clearly. Arcadia Instant offers a dual axis option for situations like these.

The following steps demonstrate how to create a line visual that uses a double axis; it is based on dataset World Life Expectancy [data source samples.world_life_expectancy].

  1. Start a new visual based on dataset World Life Expectancy [data source samples.world_life_expectancy]; see Creating Visuals.
  2. In the visuals menu, choose the Lines visual type.
  3. Populate the shelves from the available fields (Dimensions, Measures, and so on) in the Data menu.

    • Under Dimensions, select year and place it on the X Axis shelf. Specify ascending order, and alias the field as 'Year'.
    • Under Measures, select life_expectancy and place it on the Y Axis shelf. Alias it.
    • Under Measures, select Population and place it on the Colors shelf. Alias it, too.
  4. Click Refresh Visual.

    The line visual appears.

    It is impossible to see the values on the life expectancy line because the population line sets the scale for the Y axis.

    In this case, the label does not correspond to the scale shown, because this information comes from the Y axis shelf.

    Linear Plot of Population and Life Expectancy, on the Same Axis
  5. On the Colors shelf, on sum(population) field, click the icon (down arrow), select Axis, and then select Secondary Axis.

    Assigning a Measure to the Secondary Axis.
  6. Click Refresh Visual.
  7. The two lines can now be seen clearly.

    Notice that there is now a vertical axis both on the left and the right side of the visual.

    For convenience, the color of the axis labels match the line.

    Linear Plot of Population and Life Expectancy, Each on its own Axis
  8. Save the visual as World Population - Dual Lines.

Contrast this approach with plotting multiple measures as trellised charts, Trellis on Measures.