Contour plots also called level plots are a tool for doing multivariate analysis and visualizing 3-D plots in 2-D space. If we consider X and Y as our variables we want to plot then the response Z will be plotted as slices on the X-Y plane due to which contours are sometimes referred as
Z-slices or iso-response.Contour plots are widely used to visualize density, altitudes or heights of the mountain as well as in the meteorological department. Due to such wide usage
matplotlib.pyplot provides a method
contour to make it easy for us to draw contour plots.
matplotlib.pyplot.contour
The
matplotlib.pyplot.contour() are usually useful when
Z = f(X, Y) i.e Z changes as a function of input X and Y. A
contourf() is also available which allows us to draw filled contours.
Syntax: matplotlib.pyplot.contour([X, Y, ] Z, [levels], **kwargs)Parameters:X, Y: 2-D numpy arrays with same shape as Z or 1-D arrays such that len(X)==M and len(Y)==N (where M and N are rows and columns of Z)Z: The height values over which the contour is drawn. Shape is (M, N)levels: Determines the number and positions of the contour lines / regions.Returns: QuadContourSet
Below examples illustrate the
matplotlib.pyplot.contour() function in matplotlib.pyplot:
Example #1: Plotting of Contour using
contour() which only plots contour lines.
Python3 1==# Implementation of matplotlib functionimportmatplotlib.pyplotaspltimportnumpyasnpfeature_x=np.arange(0,50,2)feature_y=np.arange(0,50,3)# Creating 2-D grid of features[X,Y]=np.meshgrid(feature_x,feature_y)fig,ax=plt.subplots(1,1)Z=np.cos(X/2)+np.sin(Y/4)# plots contour linesax.contour(X,Y,Z)ax.set_title('Contour Plot')ax.set_xlabel('feature_x')ax.set_ylabel('feature_y')plt.show()
Example #2: Plotting of contour using
contourf() which plots filled contours.
Python3 1==# Implementation of matplotlib functionimportmatplotlib.pyplotaspltimportnumpyasnpfeature_x=np.linspace(-5.0,3.0,70)feature_y=np.linspace(-5.0,3.0,70)# Creating 2-D grid of features[X,Y]=np.meshgrid(feature_x,feature_y)fig,ax=plt.subplots(1,1)Z=X**2+Y**2# plots filled contour plotax.contourf(X,Y,Z)ax.set_title('Filled Contour Plot')ax.set_xlabel('feature_x')ax.set_ylabel('feature_y')plt.show()