Create a Scatter Plot in Python with Matplotlib

Scatter plots are great for visualizing data points in two dimensions. They’re particularly useful for showing correlations and groupings in data. In this tutorial, we’ll look at how to create a scatter plot in python using matplotlib.

How to make a scatter plot with Matplotlib?

Matplotlib is a library in python used for visualizing data. It offers a range of different plots and customizations. In matplotlib, you can create a scatter plot using the pyplot’s scatter() function. The following is the syntax:

import matplotlib.pyplot as plt
plt.scatter(x_values, y_values)

Here, x_values are the values to be plotted on the x-axis and y_values are the values to be plotted on the y-axis.

Examples

Let’s look at some of the examples of plotting a scatter diagram with matplotlib.

1. Scatter plot with default parameters

We have the data for heights and weights of 10 students at a university and want to plot a scatter plot of the distribution between them. The data is present in two lists. One having the height and the other having the corresponding weights of each student.

import matplotlib.pyplot as plt

# height and weight data
height = [167, 175, 170, 186, 190, 188, 158, 169, 183, 180]
weight = [65, 70, 72, 80, 86, 94, 50, 58, 78, 85]

# plot a scatter plot
plt.scatter(weight, height)
plt.show()

Output:

We get a scatter chart with data points plotted on a chart with weights on the x-axis and heights on the y-axis. From the chart, we can see that there’s a positive correlation in the data between height and weight.

2. Customize the scatter plot formatting

The scatter plot that we got in the previous example was very simple without any formatting. Matplotlib comes with number of different formatting options to customize your charts. Let’s add some formatting to the above chart.

a) Add axis labels and chart title to the chart

Matplotlib’s pyplot has handy functions to add axis labels and title to your chart. Let’s add them to the chart created above:

import matplotlib.pyplot as plt

# height and weight data
height = [167, 175, 170, 186, 190, 188, 158, 169, 183, 180]
weight = [65, 70, 72, 80, 86, 94, 50, 58, 78, 85]

# plot a scatter plot
plt.scatter(weight, height)
# set axis lables
plt.xlabel("Weight (Kg)")
plt.ylabel("Height (cm)")
# set chart title
plt.title("Height v/s Weight")
plt.show()

Output:

b) Change marker and marker size

The scatter plots above have round markers. You can alter the shape of the marker with the marker parameter and size of the marker with the s parameter of the scatter() function. For instance, to make the markers start-shaped instead of the round with larger size:

import matplotlib.pyplot as plt

# height and weight data
height = [167, 175, 170, 186, 190, 188, 158, 169, 183, 180]
weight = [65, 70, 72, 80, 86, 94, 50, 58, 78, 85]

# plot a scatter plot with star markers
plt.scatter(weight, height, marker='*', s=80)
# set axis lables
plt.xlabel("Weight (Kg)")
plt.ylabel("Height (cm)")
# set chart title
plt.title("Height v/s Weight")
plt.show()

Output:

3. Scatter plot colored by category

You can also have different colors for different data points in matplotlib’s scatter plot. This is very useful if your data points belonging to different categories. For instance, in the above example, if we add data corresponding to the nationalities of the students say country A and B and want to display each country with a different color:

import matplotlib.pyplot as plt

# height, weight and country data
height = [167, 175, 170, 186, 190, 188, 158, 169, 183, 180]
weight = [65, 70, 72, 80, 86, 94, 50, 58, 78, 85]
country = ['A', 'A', 'B', 'B', 'B', 'B', 'A', 'A', 'B', 'A']

# color map for each category
colors = {'A':'orange', 'B':'blue'}
color_ls = [colors[i] for i in country]

# plot
plt.scatter(weight, height, c=color_ls)
plt.xlabel("Weight (Kg)")
plt.ylabel("Height (cm)")
plt.title("Height v/s Weight")
plt.show()

Output:

You can see that data points for A are colored orange while data points for B are blue. This gives another insight that students from country A tend to have lower height and weight than students from B based on the given data.

For more on the maplotlib scatter plot function, refer to its documentation.

With this, we come to the end of this tutorial. The code examples and results presented in this tutorial have been implemented in a Jupyter Notebook with a python (version 3.8.3) kernel having matplotlib version 3.2.2