Legend placement options in Matplotlib - Step-by-Step Execution

Concept Flow - Legend placement options

Create plot with data

↓

Call plt.legend()

↓

Specify location parameter

↓

Legend placed on plot

↓

Show plot with legend

The flow shows creating a plot, calling legend with a location option, placing the legend accordingly, and displaying the plot.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1,2,3], label='Line')
plt.legend(loc='upper right')
plt.show()

This code plots a line and places the legend at the upper right corner.

Execution Table

Step	Action	Parameter	Effect	Legend Position
1	Plot data	data=[1,2,3]	Line plotted	No legend yet
2	Call legend()	loc='upper right'	Legend created	Upper right corner
3	Show plot	None	Plot displayed with legend	Upper right corner
4	Call legend()	loc='lower left'	Legend moved	Lower left corner
5	Show plot	None	Plot displayed with legend	Lower left corner
6	Call legend()	loc='best'	Legend auto-placed	Best location chosen by matplotlib
7	Show plot	None	Plot displayed with legend	Best location
8	Call legend()	loc='center'	Legend centered	Center of plot
9	Show plot	None	Plot displayed with legend	Center
10	Call legend()	loc='right'	Legend placed on right	Right side
11	Show plot	None	Plot displayed with legend	Right side
12	Call legend()	loc='none'	No legend shown	No legend
13	Show plot	None	Plot displayed without legend	No legend

💡 All legend placement options demonstrated and plot shown accordingly.

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 6	After Step 8	After Step 10	After Step 12
legend_location	None	'upper right'	'lower left'	'best'	'center'	'right'	'none'

Key Moments - 3 Insights

Why does the legend sometimes overlap the plot lines?

When using fixed locations like 'center', the legend can cover data. Using 'best' lets matplotlib find a place with least overlap, as shown in execution_table rows 6 and 7.

What happens if I set loc='none'?

No legend is shown on the plot, as seen in execution_table rows 12 and 13 where the legend disappears.

How can I place the legend on the right side of the plot?

Using loc='right' places the legend on the right side of the plot, demonstrated in rows 10 and 11.

Visual Quiz - 3 Questions

Look at the execution_table, what is the legend position after step 4?

A Upper right corner

B Lower left corner

C Center of plot

D No legend

💡 Hint

Check the 'Legend Position' column for step 4 in execution_table.

At which step does matplotlib automatically choose the best legend location?

A Step 2

B Step 8

C Step 6

D Step 10

💡 Hint

Look for 'best' in the 'Parameter' column in execution_table.

If you want no legend to appear, which loc value should you use according to the table?

A 'none'

B 'best'

C 'upper right'

D 'right'

💡 Hint

Check the effect of loc='none' in execution_table rows 12 and 13.

Concept Snapshot

plt.legend(loc=location) places the legend.
Common loc values: 'upper right', 'lower left', 'best', 'center', 'right'.
'best' auto-finds a clear spot.
'none' hides the legend.
Legend can be inside or outside the plot area.

Full Transcript

This lesson shows how to place legends in matplotlib plots using the loc parameter in plt.legend(). We start by plotting data, then call plt.legend() with different loc values like 'upper right', 'lower left', 'best', 'center', and 'right'. Each placement changes where the legend appears on the plot. The 'best' option lets matplotlib pick a spot that avoids covering data. Using 'none' hides the legend. The execution table traces each step showing the legend's position. Variable tracker shows how the legend_location changes. Key moments clarify common confusions like overlapping legends and placing legends on the right side of the plot. The quiz tests understanding of legend positions at different steps. The snapshot summarizes how to use legend placement options simply.

Practice

1. What does the loc parameter control in a matplotlib legend?

easy

A. The type of plot displayed

B. The color of the legend box

C. The font size of the legend text

D. The position of the legend inside or outside the plot area

Solution

1. Step 1: Understand the role of loc in legend placement

   The loc parameter specifies where the legend appears relative to the plot, such as 'upper right' or 'lower left'.

2. Step 2: Differentiate from other legend properties

   Other properties like color or font size are controlled by different parameters, not loc.

3. Final Answer:

   The position of the legend inside or outside the plot area -> Option D

4. Quick Check:

   Legend position = loc [OK]

Hint: Remember: loc sets legend position, not style [OK]

Common Mistakes:

• Confusing loc with color or font size
• Thinking loc controls plot type
• Assuming loc changes data points

2. Which of the following is the correct syntax to place a legend at the lower center outside the plot using loc and bbox_to_anchor?

easy

A. plt.legend(loc='lower center', bbox_to_anchor=(0.5, -0.1))

B. plt.legend(loc='center lower', bbox_to_anchor=(0.5, -0.1))

C. plt.legend(location='lower center', bbox_to_anchor=(0.5, -0.1))

D. plt.legend(loc='lower center', bbox_to_anchor=[0.5, -0.1])

Solution

1. Step 1: Check correct parameter names and values

   The parameter for legend position is loc, and the value 'lower center' is valid. The bbox_to_anchor expects a tuple for coordinates.

2. Step 2: Identify syntax errors in options

   plt.legend(loc='center lower', bbox_to_anchor=(0.5, -0.1)) uses 'center lower' which is invalid. plt.legend(location='lower center', bbox_to_anchor=(0.5, -0.1)) uses 'location' instead of 'loc'. plt.legend(loc='lower center', bbox_to_anchor=[0.5, -0.1]) uses a list instead of a tuple for bbox_to_anchor.

3. Final Answer:

   plt.legend(loc='lower center', bbox_to_anchor=(0.5, -0.1)) -> Option A

4. Quick Check:

   Correct loc and tuple bbox_to_anchor = plt.legend(loc='lower center', bbox_to_anchor=(0.5, -0.1)) [OK]

Hint: Use loc='position' and bbox_to_anchor=(x, y) tuple [OK]

Common Mistakes:

• Using wrong parameter name 'location' instead of 'loc'
• Swapping order in loc value like 'center lower'
• Passing list instead of tuple for bbox_to_anchor

3. What will be the effect of this code snippet?

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], label='Line')
plt.legend(loc='upper left', bbox_to_anchor=(1, 1))
plt.show()

medium

A. Legend appears inside the plot at upper left corner

B. Legend appears outside the plot at the upper left corner

C. Legend appears outside the plot at the top-right corner

D. Code raises an error due to invalid bbox_to_anchor

Solution

1. Step 1: Understand loc and bbox_to_anchor interaction

   The loc='upper left' sets the legend's anchor point to its upper left corner, and bbox_to_anchor=(1,1) places that anchor point at the top-right corner of the axes.

2. Step 2: Determine legend position

   With the legend's upper left anchored at the plot's top-right corner (1,1), the legend extends to the right, appearing outside the plot at the top-right corner.

3. Final Answer:

   Legend appears outside the plot at the top-right corner -> Option C

4. Quick Check:

   loc='upper left' + bbox_to_anchor=(1,1) = outside top-right [OK]

Hint: bbox_to_anchor moves legend outside; loc sets anchor point [OK]

Common Mistakes:

• Assuming legend stays inside plot
• Confusing loc and bbox_to_anchor roles
• Expecting an error from bbox_to_anchor values

4. Identify the error in this code that tries to place the legend outside the plot at the bottom right:

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], label='Data')
plt.legend(loc='bottom right', bbox_to_anchor=(1, 0))
plt.show()

medium

A. Label parameter is incorrect

B. Invalid loc value 'bottom right'

C. Missing plt.show() call

D. bbox_to_anchor must be a list, not a tuple

Solution

1. Step 1: Check valid loc values

   Matplotlib does not recognize 'bottom right' as a valid loc string. The correct value is 'lower right'.

2. Step 2: Verify other parameters

   bbox_to_anchor accepts tuples, plt.show() is present, and label syntax is correct.

3. Final Answer:

   Invalid loc value 'bottom right' -> Option B

4. Quick Check:

   loc must be valid string like 'lower right' [OK]

Hint: Use exact loc strings like 'lower right', not 'bottom right' [OK]

Common Mistakes:

• Using incorrect loc names
• Thinking bbox_to_anchor needs list
• Forgetting plt.show()

5. You want to place a legend outside the plot on the right side, vertically centered. Which combination of loc and bbox_to_anchor achieves this?

hard

A. loc='center left', bbox_to_anchor=(1, 0.5)

B. loc='center right', bbox_to_anchor=(1, 0.5)

C. loc='center left', bbox_to_anchor=(0, 0.5)

D. loc='upper right', bbox_to_anchor=(1, 0.5)

Solution

1. Step 1: Understand legend anchor and position

   To place the legend outside on the right, the anchor point should be on the left side of the legend box, so it aligns just outside the plot.

2. Step 2: Choose correct loc and bbox_to_anchor

   loc='center left' anchors the legend's left center, and bbox_to_anchor=(1, 0.5) places it just outside the plot on the right, vertically centered.

3. Final Answer:

   loc='center left', bbox_to_anchor=(1, 0.5) -> Option A

4. Quick Check:

   Anchor left + bbox at right center = legend outside right [OK]

Hint: Anchor legend left side to place it outside right [OK]

Common Mistakes:

• Using loc='center right' which anchors wrong side
• Setting bbox_to_anchor x=0 to place outside right
• Using upper right loc for vertical center