What are surface plots?

A plot for a Response or z-variable based on a mesh determined from two input factors, an x-variable and a y-variable. A three-dimensional graph is required to visualize the relationship between three variables. Surface plots are diagrams that combine three-dimensional data with two-dimensional elements. Surface plots are diagrams that show the functional relationship of independent and dependent variables.

Surface Plot is used when you have a model that has been stored and want to show how the fitted response compares to two continuous variables. The surface plot shows the three-dimensional relationship in two dimensions. The variables on the x and y-axes are represented by smooth surfaces, while the response variable (z), is shown as a surface plot.

Analysts at a solar energy company, for example, want to plot heat flux and the positions of the east- and south-central focal points. An analysis was done to determine the relationship between heat flux and focal points.

Minitab stores your model in its worksheet automatically. You can find more information in the Stored Model overview.

The key results of the Surface Plot are explained

A surface plot is used to determine how the fitted responses relate to continuous variables that are derived from a model equation. A surface plot is a wireframe graph with three dimensions that can be used to establish desired response values and operating conditions. These elements make up a surface plot:

  • Predictors for the x-and y-axes.
  • The continuous surface represents the fitted response values along the z-axis.

Minitab’s display of the appropriate response values depends on which response variable you have. Minitab displays these types of fitted values

  • Response variables are continuous measures such as length and weight.
  • Response variables that have means that include counts that are consistent with the Poisson distribution (e.g., the number of samples that are defective).
  • Probabilities of response variables with only two outcomes (pass/fail)
  • Standard deviations of models that have been fitted using Analyze Variability

A surface plot only shows two continuous variables at once, so any additional variables are kept at a constant level.

A surface plot may only contain two continuous variables. Minitab will hold each variable not shown on the plot constant if a model contains more than two continuous variables. Minitab will also keep the categorical variables constant if a model contains categorical variable. These plots can only be used for fixed amounts of extra variables. The response surface can change if you adjust the holding levels. Sometimes, it can even change dramatically.

Surface plots don’t use data from the worksheet. Minitab calculates the response surface using a stored model. The model’s ability to accurately represent the true relationships between variables will determine the accuracy of the surface plot.