1.
Exploratory Data Analysis
1.3. EDA Techniques 1.3.3. Graphical Techniques: Alphabetic


Purpose: Display 3d surface on 2d plot 
A contour plot is a graphical technique for representing
a 3dimensional surface by plotting constant z slices,
called contours, on a 2dimensional format. That is, given
a value for z, lines are drawn for connecting the (x,y)
coordinates where that z value occurs.
The contour plot is an alternative to a 3D surface plot. 

Sample Plot: 
This contour plot shows that the surface is symmetric and peaks in the center. 

Definition 
The contour plot is formed by:
An additional variable may be required to specify the Z values for drawing the isolines. Some software packages require explicit values. Other software packages will determine them automatically. If the data (or function) do not form a regular grid, you typically need to perform a 2D interpolation to form a regular grid. 

Questions 
The contour plot is used to answer the question


Importance: Visualizing 3dimensional data 
For univariate data, a
run sequence plot and a
histogram are
considered necessary first steps in understanding the data.
For 2dimensional data, a scatter plot
is a necessary first step in understanding the data.
In a similar manner, 3dimensional data should be plotted. Small data sets, such as result from designed experiments, can typically be represented by block plots, DOE mean plots, and the like ("DOE" stands for "Design of Experiments"). For large data sets, a contour plot or a 3D surface plot should be considered a necessary first step in understanding the data. 

DOE Contour Plot  The DOE contour plot is a specialized contour plot used in the design of experiments. In particular, it is useful for full and fractional designs.  
Related Techniques 
3D Plot 

Software 
Contour plots are available in most general purpose statistical
software programs. They are also available in many general
purpose graphics and mathematics programs. These programs
vary widely in the capabilities for the contour plots they
generate. Many provide just a basic contour plot over
a rectangular grid while others permit color filled or
shaded contours.
Most statistical software programs that support design of experiments will provide a DOE contour plot capability. 