How to add a legend to a scatter plot in Matplotlib ?

In this article, we are going to add a legend to the depicted images using matplotlib module. We will use the matplotlib.pyplot.legend() method to describe and label the elements of the graph and distinguishing different plots from the same graph. 

Syntax: matplotlib.pyplot.legend( [“title_1”, “Title_2”],  ncol = 1 , loc = “upper left” ,bbox_to_anchor =(1, 1) )

Parameters :

• ncol: [takes int, optional parameter] the default value is 1. It represents the number of columns in legend.
• loc: [takes string, optional parameter] the default value is “best” i.e “upper left”. It represents the location of the legend. Other options can be: “best”, “upper right”, “upper left”, “lower left”, “lower right” , “right”, “center left”, “center right”, “lower center”, “upper center”, “center”.
• bbox_to_anchor: [takes a list or tuple of 2 int/float, optional parameter ]. It represents the co-ordinates of legend on the graph. Both x and y co-ordinates are mandatory to give.

Example 1: 

Python3

# import required modules
import matplotlib.pyplot as plt

# adjust coordinates
x =  [1,2,3,4,5]
y1 = [2,4,6,8,10]
y2 = [3,6,9,12,15]

# depict illustration
plt.scatter(x, y1)
plt.scatter(x,y2)

# apply legend()
plt.legend(["x*2" , "x*3"])
plt.show()

Output:

Example 2:

Python3

# impoert required modules
import matplotlib.pyplot as plt

# adjust coordinates
x =  [1,2,3,4,5]
y1 = [2,4,6,8,10]
y2 = [3,6,9,12,15]

# depict illustration
plt.scatter(x, y1)
plt.scatter(x,y2)

# apply legend()
plt.legend(["x*2" , "x*3"], ncol = 2 , loc = "lower right")
plt.show()

Output:

Example 3:

Python3

# import required modules
import matplotlib.pyplot as plt

# adjust coordinates
x =  [1,2,3,4,5]
y1 = [2,4,6,8,10]
y2 = [3,6,9,12,15]

# depict illustration
plt.scatter(x, y1)
plt.scatter(x,y2)

# apply legend()
plt.legend(["x*2" , "x*3"], bbox_to_anchor = (1 , 1))
plt.show()

Output:

Note : We may label the elements of the plot in matplotlib.pyplot.scatter() using “label” parameter. However, to show it matplotlib.pyplot.legend() must be written. 

Example 4:

Python3

# import required modules
import matplotlib.pyplot as plt
import numpy as np

# assign coordinates
x = np.arange(1, 6)
y1 = x**2
y2 = x**4

# depict illustration
plt.scatter(x, y1, label="x**2")
plt.scatter(x, y2, label="x**4")

# apply legend()
plt.legend()
plt.show()

Output:

Note: If matplotlib.pyplot.legend() is not written in code, then labels will not be shown.