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How to create a contour plot with contour lines and levels?

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by sneha@openweaver.com dot icon Updated: Jul 12, 2023

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A contour plot is a type of data visualization. It represents 3D data in a 2D space using contour lines or filled color regions. It is used in data analysis. It displays the variation and patterns of a continuous variable over a 2D domain. It represents different levels of the variable through contour lines or filled regions. It is where each line or region corresponds to a specific value.  

 

The contour lines connect points with equal values. It helps create smooth curves that follow the shape of the underlying data. The spacing between the lines indicates the variable's rate of change or gradient. It visually represents the data, revealing patterns and interest regions.  

 

It is useful in Topographic Analysis, Heatmaps, Data Interpolation, Optimization, and Decision-Making. They help analyze patterns, relationships, and variations in continuous variables. It makes them valuable for data exploration, scientific analysis, and decision-making. It can be plotted using a contour plot, including numeric and categorical data.  

 

Contour plots are most employed with numeric data. It is where the variable of interest is continuous and can take any numeric value. While contour plots are designed for numeric data, there are adaptations. It allows the visualization of categorical data as well. One approach is to use a contour or heatmap to represent categorical data on a 2D grid. Categorical data can include use types, species distribution, or customer segments.  

 

Contour plots help identify regions with high or low occurrences of specific categories. It reveals spatial patterns and highlights areas of interest. In Matplotlib, there are several contour plots that you can create to visualize your data. These include simple contour plots, smooth contour plots, and filled contour plots. When customizing this plot, various parameters help achieve the appearance.  

 

You can customize Line Style, Contour Interval, Color Map, Colorbar, Labels, and Titles. There are extra parameters for controlling colors, colorbar formatting, shading, transparency, and more. By experimenting with these parameters, you can tailor the contour plot. It suits your specific requirements and achieves the desired visual representation.  

 

In conclusion, contour plots are a powerful data visualization tool. It analyzes and interprets patterns in two-dimensional data. They help identify trends, variations, and relationships within continuous numeric data. It can also be adapted for representing categorical data.  

 

By connecting points of equal value, it provides a visual representation. It facilitates data analysis and decision-making. The contour plots help showcase the spatial distribution of a variable. It captures intricate patterns and gradients.  


Here is an example of creating contour plots with contour lines and levels.



Fig1: Preview of the output when the code is run in IDE.

Code


In this solution, we're creating contour plot with contour lines and levels.

Problems wiht contourf and levels

PythondotLines of Code : 33dotLicense : Strong Copyleft (CC BY-SA 4.0)

Dependent Libraries : 
import matplotlib.colors as mcol
import matplotlib.pyplot as plt
import numpy as np

# dummy data, a sine, 0 in the origin, 1 close to NE corner
x = np.linspace(0, 1, N)
X, Y = np.meshgrid(x, x)
R = np.sqrt(X**2+Y**2)
Z = np.sin(R*3/2)

# the levels that I want to draw on the plot,
# the levels, except for the extremes, are quite arbitrary
# as arbitrary do they seem your level specifications
levels = [0.0, .5, .6, .75, .85, .95, 1.0]
# your colormap
cmap = mcol.ListedColormap(['#2c7bb6', '#0a793a', '#77a353',
                            '#f1d499', '#c96a33', '#975114'])
# the nuber of intervals must be equal to the number of listed colors
assert(len(levels)-1==cmap.N)
# the norm that we use to map values to colors, see the docs    
norm = mcol.BoundaryNorm(levels, cmap.N)

# we are ready to plot
plt.contourf(X, Y, Z, cmap=cmap, levels=levels, norm=norm)
plt.colorbar()

# this is not necessary for your problem but it;s nice in my example    
p = plt.contour(X, Y, Z, levels=levels, colors='k')
plt.clabel(p, inline=1)

#  T H E   E N D
plt.show()

Instructions

Follow the steps carefully to get the output easily.

  1. Install Jupyter Notebook on your computer.
  2. Open the terminal and install the required libraries with the following commands.
  3. Install Numpy - pip install numpy
  4. Install matplotlib - pip install matplotlib
  5. Copy the snippet using the 'copy' button and paste it into that file.
  6. Remove the 'n' present in line number 6 to avoid any errors.
  7. Run the file using run button.


I hope you found this useful. I have added the link to dependent libraries, and version information in the following sections.


I found this code snippet by searching for "Errors while making counter plot with contourf and levels" in kandi. You can try any such use case!

Dependent Libraries

matplotlibby matplotlib

Python doticonstar image 17559 doticonVersion:v3.7.1doticon
no licences License: No License (null)

matplotlib: plotting with Python

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            matplotlibby matplotlib

            Python doticon star image 17559 doticonVersion:v3.7.1doticonno licences License: No License

            matplotlib: plotting with Python
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                      numpyby numpy

                      Python doticonstar image 23755 doticonVersion:v1.25.0rc1doticon
                      License: Permissive (BSD-3-Clause)

                      The fundamental package for scientific computing with Python.

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                                numpyby numpy

                                Python doticon star image 23755 doticonVersion:v1.25.0rc1doticon License: Permissive (BSD-3-Clause)

                                The fundamental package for scientific computing with Python.
                                Support
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                                    Security
                                      License
                                        Reuse

                                          You can also search for any dependent libraries on kandi like "matplotlib / numpy"

                                          Environment Tested


                                          I tested this solution in the following versions. Be mindful of changes when working with other versions.

                                          1. The solution is created in Python3.9.6.
                                          2. The solution is tested on numpy 1.21.5 version.
                                          3. The solution is tested on matplotlib 3.5.2 version.


                                          Using this solution, we are able to create contour plot with contour lines and levels.


                                          This process also facilities an easy to use, hassle free method to create a hands-on working version of code which would help us to create contour plot with contour lines and levels.

                                          Support


                                          1. For any support on kandi solution kits, please use the chat
                                          2. For further learning resources, visit the Open Weaver Community learning page.

                                          FAQ:  

                                          1. What are filled contour plots, and how can they be used in matplotlib?  

                                          Filled contour plots are also known as filled contour or heatmaps. They are a variation of contour plots where the regions between lines are filled with colors. It represents the magnitude or density of the underlying data. They provide a visual representation of the variable distribution across a 2D domain. Filled contour plots are useful for various applications, including:  

                                          • Visualizing density or concentration of phenomena. It includes population density, pollutant levels, or crop yields across a geographical region.  
                                          • Representing spatial data, such as elevation, temperature, or precipitation, on a map.  
                                          • Analyzing scientific data, such as contouring meteorological measurements, experimental results, or simulation outputs.  


                                          2. How is a surface plot different from a three-dimensional graph?  

                                          A surface plot is also known as a 3D surface plot or a 3D plot. It visualizes a continuous surface in a three-dimensional space. It represents the relationship between three continuous variables. They can be two independent variables on the x and y-axis and dependent on the z-axis. The surface plot displays the surface's shape, curvature, and variations. It helps in the visualization of complex three-dimensional relationships.  

                                           

                                          But a 3D graph is also called a 3D or a 3D scatter plot. It represents data points in a three-dimensional space. It visualizes the relationship between three variables. It is where each data point is defined by its values along the x, y, and z axes. Unlike a surface plot, a 3D graph presents individual data points in space. It allows for the examination of their positions and patterns.  

                                           

                                          3. How do I create a color map on my contour plot using matplotlib?  

                                          In Matplotlib, you can create a color map using the contourf() function and a specified color map. Here's a step-by-step guide on how to achieve this:  

                                          • Import the necessary libraries.  
                                          • Generate the data for the contour plot.  
                                          • Create the contour plot with a color map.  
                                          • Add a color bar.  
                                          • Customize the plot (optional).  
                                          • Display or save the plot.  

                                           

                                          4. What kind of data should be plotted along the vertical axis of a contour plot?  

                                          In a contour plot, the vertical axis represents a continuous or a response variable. It is being analyzed or predicted. The choice of data to be plotted along the vertical axis. It depends on the nature of the problem, or the type of data being analyzed. Here are a few examples of the types of data plotted along the vertical axis in contour plots:  

                                          • Elevation or Height  
                                          • Time or Date  
                                          • Response or Dependent Variable  
                                          • Concentration or Intensity  

                                           

                                          5. How can I customize the color scale for my contour plot in matplotlib?  

                                          You can customize the color scale by adjusting the color map to map the variable values to colors. Here are some ways to customize the color scale:  

                                          • Choosing a Built-in Color Map  
                                          • Creating a Custom Color Map  
                                          • Controlling the Color Range 

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