Legend

The pygmt.Figure.legend method can automatically create a legend for symbols plotted using pygmt.Figure.plot. A legend entry is only added when the label parameter is used to state the desired text. Optionally, to adjust the legend, users can append different modifiers. A list of all available modifiers can be found at https://docs.generic-mapping-tools.org/6.5/gmt.html#l-full. To create a multiple-column legend +N is used with the desired number of columns. For more complicated legends, users may want to write an ASCII file with instructions for the layout of the legend items and pass it to the spec parameter of pygmt.Figure.legend. For details on how to set up such a file, please see the GMT documentation at https://docs.generic-mapping-tools.org/6.5/legend.html#legend-codes.

import numpy as np
import pygmt

# Set up some test data
x = np.arange(-10, 10.2, 0.2)
y1 = np.sin(x) + 1.1
y2 = np.cos(x) + 1.1
y3 = np.sin(x / 2) - 1.1
y4 = np.cos(x / 2) - 1.1

# Create new Figure() object
fig = pygmt.Figure()

fig.basemap(
    projection="X10c/7c",
    region=[-10, 10, -3.5, 3.5],
    frame=["WSne", "xaf+lx", "ya1f0.5+ly"],
)

# -----------------------------------------------------------------------------
# Top: Vertical legend (one column, default)

# Use the label parameter to state the text label for the legend entry
fig.plot(x=x, y=y1, pen="1p,green3", label="sin(x)+1.1")

fig.plot(x=x, y=y2, style="c0.07c", fill="dodgerblue", label="cos(x)+1.1")

# Add a legend to the plot; place it within the plot bounding box with both
# reference ("J") and anchor ("+j") points being the Top Right (TR) corner and an
# offset of 0.2 centimeters in x and y directions; surround the legend with a box
fig.legend(position="JTR+jTR+o0.2c", box=True)

# -----------------------------------------------------------------------------
# Bottom: Horizontal legend (here two columns)

# +N sets the number of columns corresponding to the given number, here 2
fig.plot(x=x, y=y3, pen="1p,darkred,-", label="sin(x/2)-1.1+N2")

fig.plot(x=x, y=y4, style="s0.07c", fill="orange", label="cos(x/2)-1.1")

# For a multi-column legend, users have to provide the width via "+w", here it is
# set to 6 centimeters; reference and anchor points are the Bottom Right (BR) corner
fig.legend(position="JBR+jBR+o0.2c+w6c", box=True)

fig.show()