Matplotlib - Figure Object

3. Creating a Figure

The Object-Oriented approach requires creating a Figure object and adding Axes to it.

3.1 Basic Figure with Axes

fig = plt.figure()  # Creates an empty figure
 
# Adding a set of axes: [left, bottom, width, height] (range: 0 to 1)
axes = fig.add_axes([0, 0, 1, 1])  
 
# Plotting on the axes
axes.plot(x, y)
 
plt.show()

🔹 fig.add_axes([0, 0, 1, 1]):

left, bottom: Position of the axes (0 to 1)
width, height: Size of the axes (0 to 1)
left and bottom: refer to the position of the lower left corner of the axis in the entire Figure canvas (relative ratio, 0 means the far left/bottom, 1 means the far right/top).
width and height: refer to the width and height of the axis, relative to the ratio of the entire Figure canvas, the maximum can be 1, but it can exceed 1, but it will overflow the Figure canvas range

3.2 Different Data on Another Axes

fig = plt.figure()
axes = fig.add_axes([0, 0, 1, 1])
axes.plot(a, b)  # Plotting `a, b`
plt.show()

4. Adding Multiple Axes 🎭

We can add multiple axes within the same figure.

4.1 Small Plot Inside a Bigger Plot

fig = plt.figure()
 
axes1 = fig.add_axes([0, 0, 1, 1])    # Main figure (large)
axes2 = fig.add_axes([0.2, 0.2, 0.5, 0.5])  # Smaller inset figure
 
# Plot on larger figure
axes1.plot(a, b)
axes1.set_xlabel('X Label')
axes1.set_ylabel('Y Label')
axes1.set_title('Big Figure')
 
# Plot on smaller figure
axes2.plot(a, b)
axes2.set_title('Small Figure')
 
plt.show()

🎯 Key Idea:
This method gives complete control over positioning.

5. Adjusting Inset Axes 🖼️

5.1 Moving and Zooming the Smaller Figure

fig = plt.figure()
 
axes1 = fig.add_axes([0, 0, 1, 1])      # Large figure
axes2 = fig.add_axes([0.2, 0.5, 0.25, 0.25])  # Small figure moved to top-left
 
# Large Figure
axes1.plot(a, b)
axes1.set_xlabel('X Label')
axes1.set_ylabel('Y Label')
axes1.set_title('Big Figure')
 
# Small Figure (Zoomed In)
axes2.plot(a, b)
axes2.set_xlim(8,10)
axes2.set_ylim(4000,10000)
axes2.set_xlabel('X')
axes2.set_ylabel('Y')
axes2.set_title('Zoomed In')
 
plt.show()

🛠 Adjustments in axes2

set_xlim(8,10): Focus on x-range [8,10]
set_ylim(4000,10000): Focus on y-range [4000,10000]

6. Multiple Inset Plots 📊

We can keep adding more axes!

fig = plt.figure()
 
axes1 = fig.add_axes([0, 0, 1, 1])       # Full figure
axes2 = fig.add_axes([0.2, 0.5, 0.25, 0.25])  # Inset 1
axes3 = fig.add_axes([1, 1, 0.25, 0.25])  # Inset 2 (top-right corner)
 
# Large Figure
axes1.plot(a, b)
axes1.set_xlabel('X Label')
axes1.set_ylabel('Y Label')
axes1.set_title('Big Figure')
 
# Inset 1
axes2.plot(a, b)
axes2.set_xlim(8,10)
axes2.set_ylim(4000,10000)
axes2.set_xlabel('X')
axes2.set_ylabel('Y')
axes2.set_title('Zoomed In')
 
# Inset 2 (new one)
axes3.plot(a, b)
axes3.set_title('Another Small Figure')
 
plt.show()

7. Adjusting Figure Size & Resolution 📏

We can specify size and resolution while creating the figure.

fig = plt.figure(figsize=(12,8), dpi=100)  # Width=12 inches, Height=8 inches, DPI=100
axes1 = fig.add_axes([0, 0, 1, 1])
axes1.plot(a, b)
plt.show()

📌 Commonly used options

figsize=(width, height): Controls figure size.
dpi=resolution: Higher values make the image clearer.

8. Exporting Figures 📂

We can save figures as image files.

8.1 Saving as a PNG

fig = plt.figure()
axes1 = fig.add_axes([0, 0, 1, 1])
axes1.plot(a, b)
axes1.set_xlabel('X')
 
fig.savefig('figure.png', bbox_inches='tight')  # Saves as 'figure.png'

🔹 bbox_inches='tight' ensures the image is cropped properly.

8.2 Another Example

fig = plt.figure(figsize=(12,8))
axes1 = fig.add_axes([0, 0, 1, 1])  
axes2 = fig.add_axes([1, 1, 0.25, 0.25])  
 
axes1.plot(x, y)
axes2.plot(x, y)
 
fig.savefig('test.png', bbox_inches='tight')

Summary ✨

Feature	Method
Create Figure	`fig = plt.figure()`
Add Axes	`fig.add_axes([left, bottom, width, height])`
Set Labels	`axes.set_xlabel('X')`, `axes.set_ylabel('Y')`
Set Title	`axes.set_title('Title')`
Plot Data	`axes.plot(x, y)`
Zoom in on Axes	`axes.set_xlim(start, end)`, `axes.set_ylim(start, end)`
Adjust Figure Size	`fig = plt.figure(figsize=(width, height), dpi=resolution)`
Save Figure	`fig.savefig('filename.png', bbox_inches='tight')`

📌 When to use Object-Oriented Matplotlib?

When dealing with multiple plots in one figure.
When precise positioning of axes is needed.
When embedding plots inside other figures.

🪴LYC