Filled contour styles

This notebook shows how to control colour levels and encapsulate your styling choices in a reusable Style object.

import earthkit.data as ekd

import earthkit.plots as ekp

data = ekd.from_source("sample", "era5-2t-msl-1985122512.grib").to_fieldlist()
pressure = data.sel({"parameter.variable": "msl"})
temperature = data.sel({"parameter.variable": "2t"})

Specifying levels

As with contour lines, you can pass levels as a list or range:

chart = ekp.Map(domain="Europe")
chart.contourf(
    temperature,
    units="celsius",
    levels=range(-20, 30, 2),
    colors="RdYlBu_r",
)
chart.legend()
chart.land()
chart.coastlines()
chart.title()
chart.show()

Or as a dict with step and reference keys:

chart = ekp.Map(domain="Europe")
chart.contourf(
    temperature,
    units="celsius",
    levels={"step": 4, "reference": 0},
    colors="RdYlBu_r",
)
chart.legend()
chart.land()
chart.coastlines()
chart.title()
chart.show()

The extend argument

By default, data values that fall outside the range of the specified levels are not coloured — they appear as the background colour of the map. The extend argument controls whether the colourbar and the filled regions are extended to cover out-of-range values:

• extend="neither" (default) — no extension; values outside the level range are uncoloured.

• extend="min" — add a triangle at the low end of the colourbar to capture values below the lowest level.

• extend="max" — add a triangle at the high end for values above the highest level.

• extend="both" — add triangles at both ends.

Here we restrict the levels to a narrow range (−10 to 20 °C) so that some data falls outside at both ends, then compare the four options:

fig = ekp.Figure(domain="Europe", rows=2, columns=2)

for ext in ["neither", "min", "max", "both"]:
    chart = fig.add_map()
    chart.contourf(
        temperature,
        units="celsius",
        levels=range(-10, 15),
        colors="RdYlBu_r",
        extend=ext,
    )
    chart.legend()
    chart.land()
    chart.coastlines()
    chart.title(f'extend="{ext}"')
fig.show()

When using a reusable Style object, pass extend alongside the other style options:

t2m_style_extended = ekp.styles.Style(
    units="celsius",
    colors="RdYlBu_r",
    levels=range(-10, 21, 5),
    extend="both",
)

chart = ekp.Map(domain="Europe")
chart.contourf(temperature, style=t2m_style_extended)
chart.legend()
chart.land()
chart.coastlines()
chart.title()
chart.show()

Creating a reusable Style

Encapsulate all styling options in an ekp.styles.Style object so you can apply the same look to multiple maps without repeating yourself.

t2m_style = ekp.styles.Style(
    units="celsius",
    colors="RdYlBu_r",
    levels={"step": 4, "reference": 0},
)

chart = ekp.Map(domain="Europe")
chart.contourf(temperature, style=t2m_style)
chart.legend()
chart.land()
chart.coastlines()
chart.title()
chart.show()

Reusing the style on a different domain

chart = ekp.Map(domain="North Atlantic")
chart.contourf(temperature, style=t2m_style)
chart.legend()
chart.land()
chart.coastlines()
chart.title()
chart.show()

What’s next?

The next notebook shows how to combine filled contours with contour lines to highlight specific levels.