Contour Label Demo

Illustrate some of the more advanced things that one can do with contour labels.

See also the :doc:contour demo example </gallery/images_contours_and_fields/contour_demo>.

import matplotlib.pyplot as plt
import numpy as np

import matplotlib.ticker as ticker

Define our surface

delta = 0.025
x = np.arange(-3.0, 3.0, delta)
y = np.arange(-2.0, 2.0, delta)
X, Y = np.meshgrid(x, y)
Z1 = np.exp(-X**2 - Y**2)
Z2 = np.exp(-(X - 1)**2 - (Y - 1)**2)
Z = (Z1 - Z2) * 2

Make contour labels with custom level formatters

# This custom formatter removes trailing zeros, e.g. "1.0" becomes "1", and
# then adds a percent sign.
def fmt(x):
    s = f"{x:.1f}"
    if s.endswith("0"):
        s = f"{x:.0f}"
    return rf"{s} \%" if plt.rcParams["text.usetex"] else f"{s} %"


# Basic contour plot
fig, ax = plt.subplots()
CS = ax.contour(X, Y, Z)

ax.clabel(CS, CS.levels, inline=True, fmt=fmt, fontsize=10)

<a list of 7 text.Text objects>

Label contours with arbitrary strings using a dictionary

fig1, ax1 = plt.subplots()

# Basic contour plot
CS1 = ax1.contour(X, Y, Z)

fmt = {}
strs = ['first', 'second', 'third', 'fourth', 'fifth', 'sixth', 'seventh']
for l, s in zip(CS1.levels, strs):
    fmt[l] = s

# Label every other level using strings
ax1.clabel(CS1, CS1.levels[::2], inline=True, fmt=fmt, fontsize=10)

<a list of 3 text.Text objects>

Use a Formatter

fig2, ax2 = plt.subplots()

CS2 = ax2.contour(X, Y, 100**Z, locator=plt.LogLocator())
fmt = ticker.LogFormatterMathtext()
fmt.create_dummy_axis()
ax2.clabel(CS2, CS2.levels, fmt=fmt)
ax2.set_title("$100^Z$")

plt.show()

… admonition:: References

The use of the following functions, methods, classes and modules is shown in this example:

• matplotlib.axes.Axes.contour / matplotlib.pyplot.contour

• matplotlib.axes.Axes.clabel / matplotlib.pyplot.clabel

• matplotlib.ticker.LogFormatterMathtext

• matplotlib.ticker.TickHelper.create_dummy_axis