Double Y-axes

The frame parameter of the plotting methods of the pygmt.Figure class can control which axes should be plotted and possibly show annotations and tick marks. By default, all 4 axes are plotted, along with annotations and tick marks (denoted W, S, E, N). Lower case versions (w, s, e, n) can be used to denote to only plot the axes with tick marks. We can also only plot the axes without annotations and tick marks using l (left axis), r (right axis), t (top axis), b (bottom axis).

Out:

<IPython.core.display.Image object>

import numpy as np
import pygmt

# Generate common x values and two kinds of y values
x = np.linspace(1.0, 9.0, num=9)
y1 = x
y2 = x ** 2 + 110

fig = pygmt.Figure()

# Plot y1
# The bottom axis (S) is plotted with annotations and tick marks
# The top axis (t) is plotted without annotations and tick marks
fig.basemap(region=[0, 10, 0, 10], projection="X15c/15c", frame=["St", "xaf+lx"])
# The left axis (W) is plotted with customized annotations, tick marks and labels
with pygmt.config(
    MAP_FRAME_PEN="1.5p,blue",
    MAP_TICK_PEN="0.5p,blue",
    FONT_ANNOT_PRIMARY="12p,Helvetica,blue",
    FONT_LABEL="16p,Helvetica,blue",
):
    fig.basemap(frame=["W", "yaf+ly1"])

# Plot the line for y1
fig.plot(x=x, y=y1, pen="1p,blue")
# Plot points for y1
fig.plot(x=x, y=y1, style="c0.2c", color="blue", label="y1")

# Plot y2
# The right axis (E) is plotted with customized annotations, tick marks, and labels
with pygmt.config(
    MAP_FRAME_PEN="1.5p,red",
    MAP_TICK_PEN="0.5p,red",
    FONT_ANNOT_PRIMARY="12p,Helvetica,red",
    FONT_LABEL="16p,Helvetica,red",
):
    fig.basemap(region=[0, 10, 100, 200], frame=["E", "yaf+ly2"])
# Plot the line for y2
fig.plot(x=x, y=y2, pen="1p,red")
# Plot points for y2
fig.plot(x=x, y=y2, style="s0.28c", color="red", label="y2")

fig.legend(position="JTL+jTL+o0.1c", box=True)

fig.show()