Basic Display Features of Equated Plots

Types of Equated Axes

The EQUATETYPE= option of the LAYOUT OVELAYEQUATED statement manages the display of the axes. The following values are available:

FIT

X and Y axes have equal increments between tick values. The data ranges of both axes are compared to establish a common increment size. The axes can be of different lengths and have a different number of tick marks. Each axis represents its own data range. One axis can be extended to use available space in the plot area. This is the default.

EQUATE

Same as FIT except that neither axis is extended to use available space in the plot area.

SQUARE

Both the X and Y axes have the same length and the same tick values. The axis length and tick values are chosen so that the minimum and maximum of both X and Y appear in the range of values appearing on both axes.

The following example template uses the EQUATETYPE= option:

proc template;
  define statgraph mpg;
    mvar TYPE;
    begingraph;
      entrytitle "Comparison of " TYPE " Vehicle Mileage by Origin";
      entryfootnote halign=right "SASHELP.CARS"; 
      layout overlayequated / equatetype=fit;
        scatterplot x=mpg_city y=mpg_highway / group=origin
          name="s" markerattrs=(size=7px);
        referenceline x=eval(mean(mpg_city)) /
          curvelabel=eval(put(mean(mpg_city),4.1));
        referenceline y=eval(mean(mpg_highway)) /
          curvelabel=eval(put(mean(mpg_highway),4.1));
        discretelegend "s";
        layout gridded / columns=1 halign=right valign=bottom;
          entry "Reference lines at";
          entry "average overall city";
          entry "and highway mileages";
        endlayout;
      endlayout;
    endgraph;
  end;
 run;
 
 %let type=SUV;
 proc sgrender data=sashelp.cars template=mpg;
   where type="&type";
 run;

Note: This program uses several features, such as run-time macro variable resolution, EVAL expressions, and insets. All of these features are discussed in detail in other chapters.

Defining Axes for Equated Layouts

Axes for the OVERLAYEQUATED layout are similar to axes for the OVERLAY layout with the following exceptions:

Both axes are always of TYPE=LINEAR.
Some axis options that always apply to both axes are specified in a COMMONAXISOPTS= option. Some of the supported options are INTEGER, TICKVALUELIST, TICKVALUESEQUENCE, VIEWMAX, and VIEWMIN.
XAXISOPTS= and YAXISOPTS= options are supported (with a different set of suboptions from those of OVERLAY), but X2AXISOPTS= and Y2AXISOPTS= options are not supported. Some of the supported options are DISPLAY, LABEL, GRIDDISPLAY, DISPLAYSECONDARY, OFFSETMAX, OFFSETMIN, THRESHOLDMAX, THRESHOLDMIN, and TICKVALUEFORMAT.
No independent secondary (X2, Y2 ) axes are available, although secondary axes that mirror the primary axes can be displayed. The XAXIS= and YAXIS= options are ignored.

Managing Axes in an OVERLAY Layout discusses many of the axis options that are available for managing graph axes.

To illustrate how to control axes for the equated layout, we will look at a simplified version of the PPPLOT template that is supplied with PROC UNIVARIATE, which is delivered with Base SAS. The following code shows a SAS program that can be used to run PROC UNIVARIATE:

ods graphics on;

proc univariate data=sashelp.heart;
  var weight;
  ppplot / normal square;
run; 
quit;

When the code is run, it creates the following plot. The plot uses the PPPLOT template, which is stored in the BASE.UNIVARIATE.GRAPHICS folder of the SASHELP.TMPLMST item store:

In PROC UNIVARIATE, the PPPLOT statement creates a probability-probability plot (also referred to as a P-P plot or percent plot), which compares the empirical cumulative distribution function (ecdf) of a variable with a specified theoretical cumulative distribution function such as the normal. If the two distributions match, the points on the plot form a linear pattern that passes through the origin and has unit slope. Thus, you can use a P-P plot to determine how well a theoretical distribution models a set of measurements.

The supplied PPPLOT template uses several dynamics to pass in values for options, but in essence, the following template is equivalent. The dynamics for the title and axis labels have been converted into literals appropriate for this set of data.

proc template;
define statgraph pp_plot;
  begingraph;
    entrytitle "P-P Plot for Weight";
    entryfootnote halign=right "Derived from PPPLOT template";

    layout overlayequated /  equatetype=square
            xaxisopts=(label="Normal(Mu=153.09 Sigma=28.915)"
                       thresholdmin=1 thresholdmax=1)
            yaxisopts=(label="Cumulative Distribution of Weight"
                       thresholdmin=1 thresholdmax=1)
            commonaxisopts=(viewmin=0.0 viewmax=1.0) ;
 
      scatterplot x=Theoretical y=Empirical;
      lineparm x=0 y=0 slope=1 / lineattrs=GraphFit;
    endlayout;

  endgraph;
end;
run;

This simplified template produces a similar plot if it is rendered with the same data as the UNIVARIATE plot. An ODS OUTPUT statement can convert the output object from UNIVARIATE into a SAS data set:

ods graphics on;
ods select ppplot;
ods output ppplot=ppdata;
proc univariate data=sashelp.heart;
  var weight;
  ppplot / normal square;
run; 
quit;
                
proc sgrender data=ppdata
              template=pp_plot;
run;

The following template modifies the equated axes, as shown in the next graph:

 layout overlayequated /  equatetype=square
    xaxisopts=(label="Normal(Mu=153.09 Sigma=28.915)"
               thresholdmin=1 thresholdmax=1
               tickvalueformat=3.2
               display=(label tickvalues)
               displaysecondary=(tickvalues)
               griddisplay=on)
    yaxisopts=(label="Cumulative Distribution of Weight"
               thresholdmin=1 thresholdmax=1
               tickvalueformat=3.2
               display=(label tickvalues)
               displaysecondary=(tickvalues)
               griddisplay=on)
    commonaxisopts=(viewmin=0.0 viewmax=1.0
               tickvaluesequence=(start=0 end=1 increment=.25) );