Excel lets you categorize your categories. This sounds redundant, but a quick example illustrates the concept. Suppose you want to plot the data shown in Figure 21-19. (Figure 21-20 shows the resulting chart.) The series are months, and the categories are the sales offices located in different cities. The city sales are further classified by state, however. To create this multilevel chart, you simply select the data, including both columns of category information, and plot it in the usual manner. Excel recognizes the second category column and creates the appropriate subcategories.

Figure 21-19. This worksheet uses multilevel categories; city sales offices are grouped by state.

Figure 21-20. A multilevel category chart uses two or more sets of category names to label the category axis.

The capability to create multilevel charts appeared first in Excel 97, just before the Excel version that introduced PivotCharts. PivotCharts—charts derived from PivotTables—are a superior alternative to multilevel charts, but they require you to create a PivotTable, and that in turn requires you to set up your data in a particular manner. To create a PivotTable from the data shown in Figure 21-19, for example, you need to organize your worksheet like this:

After creating the PivotTable, you could generate the PivotChart shown in Figure 21-21. If the information you need to plot is relatively simple and you already have it organized in a manner not conducive to PivotTable creation, you’re probably better off using the multilevel charting capability.

Figure 21-21. PivotCharts like this are an alternative (and in most cases superior) way to plot multilevel data.