Before you can create a chart, you must have some numbers—sometimes known as data. The data, of course, is stored in the cells in a worksheet. Normally, the data that a chart uses resides in a single worksheet, but that’s not a strict requirement. A chart can use data that’s stored in any number of worksheets, and the worksheets can even be in different workbooks.
A chart is essentially an object that Excel creates upon request. This object consists of one or more data series, displayed graphically. The appearance of the data series depends on the selected chart type. For example, if you create a line chart that uses two data series, the chart contains two lines, each representing one data series. The data for each series is stored in a separate row or column. Each point on the line is determined by the value in a single cell and is represented by a marker. You can distinguish each of the lines by its thickness, line style, color, or data markers (squares, circles, and so on).
Figure 18-2 shows a line chart that plots two data series across a 12-month period. I used different data markers (squares versus circles) to identify the two series, as shown in the legend at the bottom of the chart. The chart clearly shows the sales in the Eastern Region are declining steadily, while Western Region sales are increasing at a slower rate.
A key point to keep in mind is that ...