Question
Answer and Explanation
Adding a north arrow to a Matplotlib plot enhances its readability, particularly when dealing with geospatial data. While Matplotlib doesn't have a built-in function for north arrows, it's straightforward to create one using its capabilities. Here’s how you can do it:
1. Create a Function for the North Arrow:
- Begin by defining a function that creates the north arrow graphical elements. This usually involves drawing a triangle or arrow-like shape along with the letter "N". We'll be using `matplotlib.patches.Polygon` and `matplotlib.text.Text`.
2. Define the Arrow's Coordinates and Properties:
- Calculate the coordinates of the arrow's vertices based on the size and position you want. Set colors, rotation, and other properties as needed.
3. Add the Arrow to the Plot:
- Use `ax.add_patch()` to add the arrow and text objects to your Matplotlib axes object. This places the arrow on your plot.
4. Example Code Implementation:
import matplotlib.pyplot as plt
import matplotlib.patches as patches
import matplotlib.text as text
def add_north_arrow(ax, x, y, size, color='black'):
arrow_vertices = [(x - size / 2, y - size / 2), (x + size / 2, y - size / 2), (x, y + size / 2)]
arrow = patches.Polygon(arrow_vertices, facecolor=color, edgecolor=color)
ax.add_patch(arrow)
text_x = x
text_y = y - size 0.7
north_text = text.Text(text_x, text_y, 'N', ha='center', va='top', color=color)
ax.add_artist(north_text)
# Example plot
fig, ax = plt.subplots(figsize=(6, 6))
ax.plot([0, 1, 2, 3], [2, 5, 3, 7], marker='o')
# Adding the north arrow
arrow_x = 0.9 # X position of the arrow on plot (relative)
arrow_y = 0.1 # Y position of the arrow on plot (relative)
arrow_size = 0.1 #Size of arrow relative to plot size
ax_x_range = ax.get_xlim()[1] - ax.get_xlim()[0]
ax_y_range = ax.get_ylim()[1] - ax.get_ylim()[0]
arrow_x_plot = ax.get_xlim()[0] + ax_x_range arrow_x #Absolute arrow coordinates in plot
arrow_y_plot = ax.get_ylim()[0] + ax_y_range arrow_y
arrow_size_plot = min(ax_x_range, ax_y_range) arrow_size #Arrow size in plot units
add_north_arrow(ax, arrow_x_plot, arrow_y_plot, arrow_size_plot)
plt.show()
5. Customization and Positioning:
- You can adjust the `x`, `y`, `size`, and `color` parameters in the `add_north_arrow` function to place and style the arrow according to your preferences. The example code also has a relative position implementation to keep the arrow in the desired plot corner on axis changes.
By following these steps, you can effectively add a visually appealing north arrow to your Matplotlib plots, making them clearer and more informative.