Introduction to contour lines

This notebook introduces the two main ways to draw contour lines in earthkit-plots:

  • ekp.geo.contour – the high-level, single-call API

  • Map.contour – the lower-level API that gives you full control over the map and lets you layer multiple plots

[1]:

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"})

High-level API: ekp.geo.contour

The simplest way to draw contour lines is with ekp.geo.contour. By default it uses the plasma colour map and automatically picks sensible contour levels.

[2]:

ekp.geo.contour(pressure, units="hPa", domain="Europe")

[2]:

<earthkit.plots.components.maps.Map at 0x12f6a9a90>
../../../_images/examples_examples_contour_contour-introduction_3_1.png

Automatic styles with style="auto"

For well-known meteorological variables earthkit-plots has pre-defined styles. Pass style="auto" and it will select the appropriate one automatically.

[3]:

ekp.geo.contour(pressure, units="hPa", style="auto", domain="Europe")

[3]:

<earthkit.plots.components.maps.Map at 0x16b188d90>
../../../_images/examples_examples_contour_contour-introduction_5_1.png

ekp.geo.plot does the same thing but also chooses the method (contour, filled contour, etc.) automatically:

[4]:

ekp.geo.plot(pressure, units="hPa")

[4]:

<earthkit.plots.components.maps.Map at 0x16805eb50>
../../../_images/examples_examples_contour_contour-introduction_7_1.png

Lower-level API: Map.contour

Map.contour gives you more control. You create the map first, then add layers to it. This makes it easy to combine contour lines with other plot types.

[5]:

chart = ekp.Map(domain="Europe")
chart.contour(pressure, units="hPa")
chart.land()
chart.coastlines()
chart.title()
chart.show()
../../../_images/examples_examples_contour_contour-introduction_9_0.png

Overlaying contour lines on a filled map

Because Map.contour and Map.contourf are separate calls you can freely combine them on one map.

[6]:

chart = ekp.Map(domain="Europe")
chart.contourf(temperature, units="celsius", style="auto")
chart.contour(pressure, units="hPa", style="auto")
chart.legend()
chart.land()
chart.coastlines()
chart.title()
chart.show()
../../../_images/examples_examples_contour_contour-introduction_11_0.png 
[7]:

ekp.geo.plot(data, groupby="time.valid_datetime")

[7]:

<earthkit.plots.components.maps.Map at 0x16a927cd0>
../../../_images/examples_examples_contour_contour-introduction_12_1.png 
[8]:

style = ekp.styles.Style(
    units="celsius",
    levels=range(-30, 31, 2),
    extend="both",
    cmap="turbo",
)

ekp.geo.plot(temperature, domain="Europe", style=style)

[8]:

<earthkit.plots.components.maps.Map at 0x16bc00d90>
../../../_images/examples_examples_contour_contour-introduction_13_1.png

What’s next?

The next notebook covers how to control contour levels, line widths and line styles.