About Bubble Charts

Bubble charts show two groups of numbers as a series of XY coordinates. A third set of numbers indicates the size of each datapoint, or bubble. Bubble charts show the relatedness of three different sets of values.

Each bubble must have three pieces of data related to it: its X coordinate, its Y coordinate, and its bubble size. Bubbles in one series are all the same color. You may have more than one series of bubbles on a chart.

Bubble charts should be used when you want to compare three sets of data for each series. If one or more of the three sets of data falls into categories in which you have one entry per category (for example, a statistic that happens every year or for every age group), that data is better served appearing as categories on a different type of chart.

Creating Bubble Charts

Because the data for bubble charts is complex and can be arranged in various configurations, Formula One for Java cannot create bubble charts automatically. It needs user input to define how to interpret the data. To create a bubble chart, you first create a "mock" chart using a sample data range. Then you bring up the Chart Data tab to redefine how the data should be used in the chart.

To create a bubble chart:

1. Set up the worksheet so that there are three sets of values for each bubble (the X axis value, the Y axis value, and the bubble size). You can set up your data range in any arrangement, even with non-contiguous cells. This is how the worksheet was set up for the example chart.

   
   

2. To create the chart, select the cells in the chart's data range. (Since you will later define which cells should represent which areas, it doesn't matter which cells you select.) Click on the Chart button and draw the chart onto the worksheet. For more information, see Creating a Chart.
3. Change the chart type to Bubble, as explained in Changing the Chart Type.

   The chart that appears will probably look odd, but you will fix it in the next steps.

4. CTRL + click on the chart to select it, then choose Format > Object. The Chart Data tab of the Format Object dialog will appear.
5. For a bubble chart like the one in the example, which has only one color of bubble and therefore only one series, delete all but one series by selecting unwanted series and clicking the Delete button.
6. Select a series. Fill in the Name text box with the name you want to appear for this color of bubble on the chart legend. You can enter the text of the name or a cell reference pointing to the cell that contains the name.

   Fill in the X Values, Y Values, and Sizes text boxes with range references that refer to the appropriate ranges on the worksheet. (These range references should include only numeric data, not heading or other text cells.)

   For more information about options for filling in the Chart Data tab, see Changing the Chart's Data Source.

   Here is how the Chart Data tab was filled in for the example chart.

   
   

7. For a bubble chart with more than one series, repeat step 6 for each series on the chart.
8. Click Apply to view your changes or OK to accept your changes.
9. Finish formatting the chart using the context menu options.

Sizing All the Bubbles

Formula One for Java sizes the bubbles proportionally. To set the starting point for sizing bubbles, Formula One for Java uses an internally computed default size. You can increase or decrease this default size to increase or decrease the size of all of the bubbles on the chart.

To change the relative sizes of all the bubbles on the chart:

1. Select the Format Plot option from the context menu.
2. Click on the Options tab.
3. In the Bubble frame, enter a value from 0 to 300, representing a percentage of the default bubble size.
4. Click Apply to see your changes or OK to accept your changes.

Labeling Bubbles by Size

A special data label formatting option for bubble charts allows you to display the bubble sizes in data labels.

To display data labels showing bubble sizes on a bubble chart series:

1. Select the series.
2. Select the Format Series option from the context menu.
3. Click on the Data Labels tab.
4. In the Type frame, select Show Bubble Sizes.
5. Click Apply to see your changes or OK to accept your changes.

Note The Data Labels tab also appears on the Format Plot and Format Data Point dialogs. This allows you to apply data labels showing bubble sizes to all the series on the plot or to just one selected data point. For more information, see About Data Labels.

Special Notes About Bubble Charts

Overlapping bubbles. If two or more data points have similar X and Y values, the bubbles may overlap, or one may be hidden behind another.

If the overlapping bubbles are two different colors, they are from two different series. You can fix the overlap by rearranging the order of the chart series. For information, see Changing the Order of Chart Series.

If the overlapping bubbles are the same color, they are from the same series. You can fix the overlap by rearranging the order of the rows in the chart's data source on the worksheet. Formula One for Java draws the bubbles in the order in which they appear on the worksheet, with the data in the higher worksheet rows drawn first and the data in the lower rows drawn on top of the earlier data. You can copy and paste the rows so that the data for the hidden bubble now appears in the bottom row.

The hidden bubble should automatically appear on top of the other bubbles. For information on copying and pasting worksheet cells, see Moving, Copying, and Pasting.

Bubbles extending off the plot. If the bubble size of a bubble located near the edge of the plot is large, part of that bubble may extend off the edge of the plot, as shown below. You can fix this problem by adjusting the axis scale in the Scale tab of the Format Axis dialog. For more information about adjusting axis scale, see Changing Axis Scale Settings.