Which statement is correct regarding the vertical variable in PROC GPLOT?

The vertical variable in PROC GPLOT is used to define the y-axis of the graph. When creating plots using SAS, the vertical variable represents the dependent variable that is typically measured and plotted against an independent variable on the x-axis. This is essential for visualizing relationships between variables, allowing users to see how changes in the x-axis variable might affect the values of the y-axis variable.

In a typical scatter plot or line graph, the y-axis is where the data points are positioned based on their values in relation to the vertical variable. Thus, correctly identifying it as the vertical measure in the context of PROC GPLOT is crucial for proper data visualization and analysis.

The other options reference either the x-axis, aesthetics like color, or size, which do not pertain to the definition or role of the vertical variable within this specific plotting procedure.