Adding an inset to the figure

To plot an inset figure inside another larger figure, we can use the pygmt.Figure.inset method. After a large figure has been created, call inset using a with statement, and new plot elements will be added to the inset figure instead of the larger figure.

import pygmt

Prior to creating an inset figure, a larger figure must first be plotted. In the example below, pygmt.Figure.coast is used to create a map of the US state of Massachusetts.

fig = pygmt.Figure()
fig.coast(
    region=[-74, -69.5, 41, 43],  # Set bounding box of the large figure
    borders="2/thin",  # Plot state boundaries with thin lines
    shorelines="thin",  # Plot coastline with thin lines
    projection="M15c",  # Set Mercator projection and size of 15 centimeter
    land="lightyellow",  # Color land areas light yellow
    water="lightblue",  # Color water areas light blue
    frame="a",  # Set frame with annotation and major tick spacing
)
fig.show()

The pygmt.Figure.inset method uses a context manager, and is called using a with statement. The position parameter, including the inset width, is required to plot the inset. Using the j argument, the location of the inset is set to one of the 9 anchors (bottom-middle-top and left-center-right). In the example below, BL sets the inset to the bottom left. The box parameter can set the fill and border of the inset. In the example below, +pblack sets the border color to black and +glightred sets the fill to light red.

fig = pygmt.Figure()
fig.coast(
    region=[-74, -69.5, 41, 43],
    borders="2/thin",
    shorelines="thin",
    projection="M15c",
    land="lightyellow",
    water="lightblue",
    frame="a",
)
with fig.inset(position="jBL+w3c", box="+pblack+glightred"):
    # pass is used to exit the with statement as no plotting methods are
    # called
    pass
fig.show()

When using j to set the anchor of the inset, the default location is in contact with the nearby axis or axes. The offset of the inset can be set with +o, followed by the offsets along the x- and y-axis. If only one offset is passed, it is applied to both axes. Each offset can have its own unit. In the example below, the inset is shifted 0.5 centimeters on the x-axis and 0.2 centimeters on the y-axis.

fig = pygmt.Figure()
fig.coast(
    region=[-74, -69.5, 41, 43],
    borders="2/thin",
    shorelines="thin",
    projection="M15c",
    land="lightyellow",
    water="lightblue",
    frame="a",
)
with fig.inset(position="jBL+w3c+o0.5c/0.2c", box="+pblack+glightred"):
    pass
fig.show()

Standard plotting methods can be called from within the inset context manager. The example below uses pygmt.Figure.coast to plot a zoomed out map that selectively paints the state of Massachusetts to show its location relative to other states.

fig = pygmt.Figure()
fig.coast(
    region=[-74, -69.5, 41, 43],
    borders="2/thin",
    shorelines="thin",
    projection="M15c",
    land="lightyellow",
    water="lightblue",
    frame="a",
)
# This does not include an inset fill as it is covered by the inset figure
# Inset width/height are determined by the ``region`` and ``projection``
# parameters.
with fig.inset(
    position="jBL+o0.5c/0.2c",
    box="+pblack",
    region=[-80, -65, 35, 50],
    projection="M3c",
):
    # Use a plotting method to create a figure inside the inset.
    fig.coast(
        land="gray",
        borders=[1, 2],
        shorelines="1/thin",
        water="white",
        # Use dcw to selectively highlight an area
        dcw="US.MA+gred",
    )
fig.show()