Contour line styles

This notebook shows how to customise contour levels, line widths and line styles.

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"})

Contour levels

You can specify levels in two ways.

As a range or list – useful when you know exactly which values you want:

chart = ekp.Map(domain="Europe")
chart.contour(pressure, units="hPa", levels=range(960, 1050, 4), colors="steelblue")
chart.land()
chart.coastlines()
chart.title()
chart.show()

As a dict with step and reference keys – useful when you want evenly spaced levels anchored to a round number. Here a 4 hPa step anchored at 1000 hPa ensures that isobar always appears:

chart = ekp.Map(domain="Europe")
chart.contour(
    pressure,
    units="hPa",
    levels={"step": 4, "reference": 1000},
    colors="steelblue",
)
chart.land()
chart.coastlines()
chart.title()
chart.show()

Line widths

Pass a single value or a list to linewidths. A list cycles through the values for successive contour levels – for example, to make every fourth isobar stand out:

chart = ekp.Map(domain="Europe")
chart.contour(
    pressure,
    units="hPa",
    levels={"step": 2, "reference": 1000},
    colors="black",
    linewidths=[0.4, 0.4, 0.4, 0.8],  # every 4th line is thicker
)
chart.land()
chart.coastlines()
chart.title()
chart.show()

Line styles

linestyles works the same way as linewidths – pass a list and it cycles. Here we plot 2 °C temperature contours in red, alternating solid and dashed lines:

chart = ekp.Map(domain="Europe")

chart.plot(temperature, units="celsius")

chart.contour(
    temperature,
    units="celsius",
    levels={"step": 2, "reference": 0},
    colors="red",
    linewidths=[1, 0.6],
    linestyles=["solid", "dashed"],
    legend_style=None,  # turn off the legend for this layer
)

chart.legend()

chart.land()
chart.coastlines()
chart.title()
chart.show()

What’s next?

The next notebook shows how to encapsulate all of these options into a reusable Style object.