Legend outside the plot in Matplotlib - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of placing a legend outside the plot in matplotlib?

Placing the legend outside the plot helps keep the plot area clear and uncluttered, making the data easier to see while still showing the legend information.

beginner

Which matplotlib function parameter helps to place the legend outside the plot?

The bbox_to_anchor parameter in the legend() function allows you to specify the exact position of the legend, including outside the plot area.

intermediate

How does the loc parameter work with bbox_to_anchor to position the legend outside the plot?

The loc parameter sets the anchor point of the legend box (like 'upper left'), and bbox_to_anchor sets the coordinates where this anchor point is placed, allowing precise control outside the plot.

intermediate

What is the effect of using plt.subplots_adjust(right=0.8) when placing a legend outside the plot?

It shrinks the plot area to the left, making space on the right side for the legend to be placed outside without overlapping the plot.

beginner

Show a simple code snippet to place a legend outside the plot on the right side using matplotlib.

import matplotlib.pyplot as plt

plt.plot([1, 2, 3], label='Line 1')
plt.plot([3, 2, 1], label='Line 2')
plt.legend(loc='center left', bbox_to_anchor=(1, 0.5))
plt.subplots_adjust(right=0.75)
plt.show()

Which parameter in matplotlib's legend function controls the exact position of the legend box?

A title

B bbox_to_anchor

C loc

D fontsize

The bbox_to_anchor parameter sets the exact coordinates for the legend box position.

What does setting loc='center left' do when placing a legend outside the plot?

A Removes the legend

B Centers the legend inside the plot

C Places the legend at the top right corner inside the plot

D Positions the legend's center left point at the anchor coordinates

The loc parameter defines which part of the legend box is placed at the bbox_to_anchor coordinates.

Why might you use plt.subplots_adjust(right=0.8) when placing a legend outside the plot?

A To add grid lines

B To increase the plot size

C To make room on the right side for the legend

D To change the legend font size

Adjusting the right margin shrinks the plot area, creating space for the legend outside.

If you want the legend to appear to the right outside the plot, which bbox_to_anchor coordinate is appropriate?

A (1, 0.5)

B (0, 0)

C (0.5, 0.5)

D (1, 1)

Coordinates (1, 0.5) place the legend just outside the right edge, vertically centered.

What happens if you place the legend inside the plot without adjusting the plot area?

A The legend may cover part of the data

B The plot automatically resizes

C The legend disappears

D The plot background changes color

Without adjusting, the legend can overlap and hide parts of the plot data.

Explain how to place a legend outside the plot on the right side using matplotlib. Include the key parameters and any layout adjustments needed.

Think about how to anchor the legend box and make space for it.

Describe why placing a legend outside the plot can improve the readability of a graph.

Consider what happens when the legend overlaps the plot.

Practice

1. What is the main purpose of placing a legend outside the plot in matplotlib?

easy

A. To keep the data area clear and improve readability

B. To make the plot smaller

C. To hide the legend from view

D. To change the plot colors automatically

Solution

1. Step 1: Understand legend placement

   Legends inside the plot can cover data points, making the plot hard to read.

2. Step 2: Effect of placing legend outside

   Placing the legend outside keeps the data visible and the plot clear.

3. Final Answer:

   To keep the data area clear and improve readability -> Option A

4. Quick Check:

   Legend outside = clear data area [OK]

Hint: Legend outside keeps plot data visible and neat [OK]

Common Mistakes:

• Thinking legend outside hides it
• Assuming it changes plot size automatically
• Believing it changes plot colors

2. Which of the following is the correct way to place a legend outside the plot on the right using bbox_to_anchor and loc?

easy

A. plt.legend(loc='upper left', bbox_to_anchor=(-1, 1))

B. plt.legend(loc='center', bbox_to_anchor=(0, 0))

C. plt.legend(loc='lower left', bbox_to_anchor=(0.5, 0.5))

D. plt.legend(loc='upper right', bbox_to_anchor=(1.05, 1))

Solution

1. Step 1: Understand bbox_to_anchor coordinates

   The tuple (1.05, 1) places the legend just outside the right edge at the top.

2. Step 2: Match loc with bbox_to_anchor

   Using loc='upper right' anchors the legend's upper right corner to the point (1.05, 1).

3. Final Answer:

   plt.legend(loc='upper right', bbox_to_anchor=(1.05, 1)) -> Option D

4. Quick Check:

   Right outside = bbox_to_anchor > 1 on x [OK]

Hint: Use bbox_to_anchor >1 on x with loc='upper right' for right outside [OK]

Common Mistakes:

• Using bbox_to_anchor inside plot area (less than 1)
• Mismatching loc and bbox_to_anchor
• Using negative bbox_to_anchor values incorrectly

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

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], label='Line')
plt.legend(loc='center left', bbox_to_anchor=(1, 0.5))
plt.show()

medium

A. Legend appears outside the plot on the right center

B. Legend appears inside the plot at center left

C. Legend appears below the plot

D. Code will raise an error

Solution

1. Step 1: Analyze bbox_to_anchor coordinates

   The point (1, 0.5) is at the right edge horizontally and center vertically.

2. Step 2: Understand loc='center left'

   The legend's center left side is anchored at (1, 0.5), placing it just outside the plot on the right center.

3. Final Answer:

   Legend appears outside the plot on the right center -> Option A

4. Quick Check:

   loc='center left' + bbox_to_anchor=(1,0.5) = right outside center [OK]

Hint: loc='center left' with bbox_to_anchor=(1,0.5) puts legend right outside center [OK]

Common Mistakes:

• Thinking legend is inside plot
• Confusing loc and bbox_to_anchor roles
• Expecting legend below plot

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

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], label='Data')
plt.legend(loc='outer_right', bbox_to_anchor=(1.05, 1))
plt.show()

medium

A. Missing plt.tight_layout() causes overlap

B. bbox_to_anchor coordinates are out of range

C. Invalid loc value 'outer_right' causes an error

D. No label provided for the plot

Solution

1. Step 1: Check loc parameter validity

   Matplotlib does not support 'outer_right' as a valid loc string; valid locs include 'upper right', 'center left', etc.

2. Step 2: Effect of invalid loc

   Using 'outer_right' causes a ValueError and the legend will not display.

3. Final Answer:

   Invalid loc value 'outer_right' causes an error -> Option C

4. Quick Check:

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

Hint: Use only valid loc strings like 'upper right', not 'outer_right' [OK]

Common Mistakes:

• Using invalid loc strings
• Ignoring need for plt.tight_layout()
• Forgetting to add label to plot

5. You want to place a legend outside the plot on the right without overlapping the plot or cutting off the legend text. Which combination of commands is best to achieve this?

hard

A. plt.legend(loc='upper right', bbox_to_anchor=(0.5, 0.5)); plt.show()

B. plt.legend(loc='center left', bbox_to_anchor=(1, 0.5)); plt.tight_layout()

C. plt.legend(loc='lower left', bbox_to_anchor=(-0.5, 0)); plt.tight_layout()

D. plt.legend(loc='center', bbox_to_anchor=(1.5, 1.5)); plt.show()

Solution

1. Step 1: Choose correct legend position

   loc='center left' with bbox_to_anchor=(1, 0.5) places the legend just outside the right center of the plot.

2. Step 2: Use plt.tight_layout() to avoid overlap

   Calling plt.tight_layout() adjusts the plot layout to prevent the legend from overlapping or being cut off.

3. Final Answer:

   plt.legend(loc='center left', bbox_to_anchor=(1, 0.5)); plt.tight_layout() -> Option B

4. Quick Check:

   Right outside + tight_layout = no overlap [OK]

Hint: Use bbox_to_anchor outside + plt.tight_layout() to avoid overlap [OK]

Common Mistakes:

• Not using plt.tight_layout() causing overlap
• Placing legend inside plot by wrong bbox_to_anchor
• Using bbox_to_anchor with negative values incorrectly