Regular lat-lon grid — plotting methods

The regular lat-lon grid (regular_ll) is the most familiar grid type in meteorology: points are evenly spaced in both latitude and longitude, forming a uniform rectangular mesh. ERA5 reanalysis data is distributed on a 0.25° × 0.25° regular lat-lon grid.

Because the grid is regular, all three plotting methods work natively without any interpolation step:

Method	How it works	Best for
grid_cells	Draws each grid point as a rectangular cell	Seeing exact cell geometry
point_cloud	Plots a coloured marker at each grid point	Quick inspection
contourf	Draws filled contours directly on the grid	Smooth, publication-quality maps

This notebook uses an ERA5 0.25° 2-metre temperature field.

import earthkit.data as ekd

import earthkit.plots as ekp

data = ekd.from_source("sample", "era5-2t-msl-1985122512.grib").to_fieldlist()
temperature = data[0]

Shared style

A single Style object keeps the colour scale consistent across all panels.

style = ekp.styles.Style(levels=range(-20, 31, 2), colors="Spectral_r", units="celsius")

All methods side-by-side

We zoom to Europe where the 0.25° cell size is large enough to be visible in grid_cells and point_cloud.

figure = ekp.Figure(rows=2, columns=2, domain=["France", "Spain"])

for method in ["point_cloud", "grid_cells", "contourf", "grid_points"]:
    subplot = figure.add_map()
    getattr(subplot, method)(data, style=style)
    subplot.title(method)

figure.coastlines()
figure.gridlines()

figure.title("Plotting regular lat-lon grid data with various methods")

figure.legend(location="right")

figure.show()

What to notice

• ``grid_cells`` shows perfectly uniform rectangular cells — the hallmark of the regular lat-lon grid. Unlike HEALPix or reduced Gaussian grids, every cell has the same angular width, though their physical area shrinks towards the poles.

• ``point_cloud`` at 0.25° resolution is dense enough that the dots form a nearly continuous field. The uniform spacing is clearly visible compared to the irregular spacing of the reduced Gaussian grid.

• ``contourf`` is typically the best choice for regular lat-lon data in final figures: it requires no interpolation and produces clean, smooth contours directly from the grid values.