Overlaying Plots

Creating Plots

Overlaying Plots

In this lesson so far, you have created one plot at a time in your PROC GPLOT steps. You can also produce multiple plots on a single set of axes by specifying multiple plot requests and the OVERLAY option in the PLOT statement.

General form, simple PLOT statement for overlaid plots:

PLOT vertical-variable-1*horizontal-variable
vertical-variable-2*horizontal-variable /
OVERLAY;

where

vertical-variable-1 is the first variable plotted on the vertical axis
vertical-variable-2 is the second variable plotted on the vertical axis
horizontal-variable is the variable plotted on the horizontal axis
OVERLAY specifies that the two plots are to overlay on one set of axes.

When you specify the OVERLAY option, the horizontal variable must be the same for both plots. Otherwise, an error will result.

The PLOT statement below, for example, plots the number of patients in exercise therapy by month and the number of treadmill tests by month. The OVERLAY option overlays the plots on the same set of axes.

     proc gplot data=clinic.totals2000; 
          plot therapy*month treadmill*month / overlay;
     run;      |<--pair1-->| |<---pair2--->|

The PROC GPLOT step creates the overlaid plots below. Note that the vertical axis is labeled with the name of the first Y variable.

Overlaid plots.

If the OVERLAY option were not specified, each plot request would generate a separate graph.