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What Kind of graph should I use?

Graphics Server offers you more than a dozen kinds of graphs, most with a variety of subtypes and styling options. In some cases only one graph type will fit the data you want to chart, but more often you'll have a choice of several types for displaying any given data. The art lies in choosing the graph type that illustrates or explains the data most effectively.

This chapter provides a brief introduction to each of Graphics Server's graph offerings, with some guidelines to help you choose the type of graph best suited to your data.

Terms you should know

X axis, Y axis, and Z axis. Most graphs are drawn on a grid whose scales are shown by two or three guidelines called axes. The horizontal guideline is called the X axis, the vertical guideline the Y axis, and the depth guideline (in three-dimensional graphs) the Z axis.

Data point. In most cases, we can define a data point as the intersection of two or more variables. For example, if the quantity of widgetssold in March is 45, then the data point is the intersection of the variables quantity sold (whose value happens to be 45) and month (whose value happens to be March).

Keep in mind that a data point doesn't necessarily appear as a point (or dot) on a graph. Depending on the type of graph, a single data point can be represented by a dot, a bar, a pie slice, an unmarked position on a curve, or some other kind of graphic--or it may not be shown at all. Data set. A data set is a group of related data points. Consider these data points for widget sales:

The five data points form a data set we can call widget sales YTD.

Independent variable and dependent variable. If a data point is at the intersection of two variables and the value of one variable determines the value of the other, then the first is called the independent variable and the other the dependent variable.

In the widget sales YTD data set described above, month is the independent variable and quantity sold is the dependent variable (because it depends on, or is identified by, the value for month).

In most graphs drawn on an X-Y grid, the independent variable is graphed along the X axis and the dependent variable along the Y axis. A graph of our widget sales data set would look like this: