Normally, you can see only one picture at a time in the graphics window; i.e., as one plot is generated, the previous plot is erased. Sometimes, however, you may want to see two plots overlaid. For example, you may want to plot vectors and pressure contours on the same plot (see Figure 28.2.1). You can do this by turning on the Overlays option (and clicking Apply) in the Scene Description panel.
Once overlaying is enabled, subsequent graphics that you generate will be displayed on top of the existing display in the active graphics window. To generate a plot without overlays, you must turn off the Overlays option in the Scene Description panel (and remember to click Apply).
When you are overlaying multiple graphics, the captions and color scale that will appear in the latest display are those that correspond to the most recently drawn graphic.
Note that when overlaying is enabled, it will apply to all graphics windows, including those that are not yet open. Turning overlays on and off does so for all graphics windows, not just for the active window. That is, if you enable overlays, open a new graphics window (as described in Section 28.2.2), and then generate two or more graphics in that window, they will be overlaid.