NCL_tm_1.py

Note: This script is aimed at demonstrating the explicit handling of tick marks, their locations, labels, etc.; therefore, the use of geocat-viz convenience functions is minimized here to show such tick management functions directly throughout this script.

This script illustrates the following concepts:

• Setting the minimum/maximum value of the Y axis in an XY plot

• Changing the width and height of a plot

• Forcing a tickmark label at beginning of X axis

See following URLs to see the reproduced NCL plot & script:

• Original NCL script: https://www.ncl.ucar.edu/Applications/Scripts/tm_1.ncl

• Original NCL plot: https://www.ncl.ucar.edu/Applications/Images/tm_1_1_lg.png and https://www.ncl.ucar.edu/Applications/Images/tm_1_2_lg.png

Import packages:

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.ticker import FixedLocator, FormatStrFormatter

import geocat.viz as gv

Generate data:

# Note that range() top value is not included in the returned array of values.
x_data = np.arange(1950, 2006)
nyears = x_data.size
y_data = np.random.uniform(-4, 4, nyears)

# Print out a formatted message; note the starting 'f' for the string.
print(
    f"There are { len(x_data) } values in x_data, and { len(y_data) } values in y_data."
)

There are 56 values in x_data, and 56 values in y_data.

Plot 1

# Generate figure (set its size (width, height) in inches) and axes
plt.figure(1, figsize=(8, 3.5))
ax = plt.gca()

# format ytick labels
ax.yaxis.set_major_formatter(FormatStrFormatter('%.1f'))

# Use geocat.viz.util convenience function to add minor and major tick lines
gv.add_major_minor_ticks(ax,
                         x_minor_per_major=5,
                         y_minor_per_major=4,
                         labelsize=16)

# Plot data and set the X axis limits.
plt.plot(x_data, y_data, color='grey', linewidth=0.5)

# Usa geocat.viz.util convenience function to set axes parameters without calling several matplotlib functions
# Set axes limits
gv.set_axes_limits_and_ticks(ax,
                             xlim=(min(x_data) - 1, max(x_data) + 1),
                             ylim=(-4.5, 4.5))

# Draw plot on the screen
plt.tight_layout()
plt.show()

Plot 2 (forced tickmark label at the beginning of X axis)

# Generate figure (set its size (width, height) in inches) and axes
plt.figure(2, figsize=(8, 3.5))
ax = plt.gca()

# Set xtick locations
xticks = [1949, 1959, 1969, 1979, 1989, 1999]
ax.xaxis.set_major_locator(FixedLocator(xticks))

# format ytick labels
ax.yaxis.set_major_formatter(FormatStrFormatter('%.1f'))

# Use geocat.viz.util convenience function to add minor and major tick lines
gv.add_major_minor_ticks(ax,
                         x_minor_per_major=4,
                         y_minor_per_major=4,
                         labelsize=16)

# Line-plot data
plt.plot(x_data, y_data, color='grey', linewidth=0.5)

# Use geocat.viz.util convenience function to set axes parameters without calling several matplotlib functions
# Set axes limits, and tick values on x-axes.
gv.set_axes_limits_and_ticks(ax,
                             xlim=(min(x_data) - 1, max(x_data) + 1),
                             ylim=(-4.5, 4.5))

# Draw plot on the screen
plt.tight_layout()
plt.show()