Scale bar

The the pygmt.Figure.scalebar method can be used to add a scale bar to a map. This example shows how such a scale bar can be customized.

import pygmt
from pygmt.params import Box, Position

# Create a new Figure instance
fig = pygmt.Figure()

# Mercator projection with 10 centimeters width
fig.basemap(region=[-45, -25, -15, 0], projection="M0/0/10c", frame=["WSne", "af"])

# -----------------------------------------------------------------------------
# Top Left: Add a plain scale bar
# It is placed based on geographic coordinates 42° West and 1° South,
# applies at the reference point (scale_loc is not used and by default False), and
# represents a length of 500 kilometers
fig.scalebar(length="500k", position=Position((-42, -1), cstype="mapcoords"))

# -----------------------------------------------------------------------------
# Top Right: Add a fancy scale bar
# It is placed based on normalized bounding box coordinates
# Use a fancy style to get a scale bar that looks like train tracks
# Add the distance unit to the single distance values
fig.scalebar(
    position=Position((0.8, 0.95), cstype="boxcoords"),
    length="500k",
    fancy=True,
    unit=True,
)

# -----------------------------------------------------------------------------
# Bottom Left: Add a thick scale bar
# Adjust the GMT default parameter MAP_SCALE_HEIGHT locally (the change applies
# only to the code within the "with" statement)
# It applies at the middle of the map (scale_loc is set to True)
# Without providing a text, the label parameter adds the distance unit as label
with pygmt.config(MAP_SCALE_HEIGHT="10p"):
    fig.scalebar(
        position=Position((0.2, 0.15), cstype="boxcoords"),
        scale_loc=True,
        length="500k",
        fancy=True,
        label=True,
    )

# -----------------------------------------------------------------------------
# Bottom Right: Add a scale bar valid for a specific location
# It is placed at BottomRight using MiddleRight as anchor point with an offset
# of 1 centimeter in both x- and y-directions
# It applies at -7° South
# A customized label is added via the label parameter
fig.scalebar(
    position=Position("BR", anchor="MR", offset=1),
    scale_loc=-7,
    length="500k",
    fancy=True,
    unit=True,
    label="valid at 7° S",
)

fig.show()

The box parameter allows surrounding the scale bar. This can be useful when adding a scale bar to a colorful map to improve contrast and readability.

fig = pygmt.Figure()

fig.basemap(region=[-45, -25, -15, 0], projection="M10c", frame=["WSne", "af"])
fig.coast(land="tan", water="steelblue")
fig.scalebar(
    position=Position("BL", cstype="inside", offset=1),
    scale_loc=-7,
    length="500k",
    fancy=True,
    label="km",
    label_alignment="right",
    # Fill the box in white with a transparency of 30 percent, add a solid
    # outline in darkgray (gray30) with a thickness of 0.5 points, and use
    # rounded edges with a radius of 3 points
    box=Box(fill="white@30", pen="0.5p,gray30,solid", radius="3p"),
)

fig.show()