matplotlib.pyplot.pcolormesh — Matplotlib 3.9.0 documentation (2024)

Create a pseudocolor plot with a non-regular rectangular grid.

Call signature:

pcolormesh([X, Y,] C, **kwargs)

X and Y can be used to specify the corners of the quadrilaterals.

Parameters:

Carray-like

The mesh data. Supported array shapes are:

• (M, N) or M*N: a mesh with scalar data. The values are mapped tocolors using normalization and a colormap. See parameters norm,cmap, vmin, vmax.

• (M, N, 3): an image with RGB values (0-1 float or 0-255 int).

• (M, N, 4): an image with RGBA values (0-1 float or 0-255 int),i.e. including transparency.

The first two dimensions (M, N) define the rows and columns ofthe mesh data.

X, Yarray-like, optional

The coordinates of the corners of quadrilaterals of a pcolormesh:

(X[i+1, j], Y[i+1, j]) (X[i+1, j+1], Y[i+1, j+1]) ●╶───╴● │ │ ●╶───╴● (X[i, j], Y[i, j]) (X[i, j+1], Y[i, j+1])

Note that the column index corresponds to the x-coordinate, andthe row index corresponds to y. For details, see theNotes section below.

If shading='flat' the dimensions of X and Y should be onegreater than those of C, and the quadrilateral is colored dueto the value at C[i, j]. If X, Y and C have equaldimensions, a warning will be raised and the last row and columnof C will be ignored.

If shading='nearest' or 'gouraud', the dimensions of Xand Y should be the same as those of C (if not, a ValueErrorwill be raised). For 'nearest' the color C[i, j] iscentered on (X[i, j], Y[i, j]). For 'gouraud', a smoothinterpolation is carried out between the quadrilateral corners.

If X and/or Y are 1-D arrays or column vectors they will beexpanded as needed into the appropriate 2D arrays, making arectangular grid.

cmapstr or Colormap, default: rcParams["image.cmap"] (default: 'viridis')

The Colormap instance or registered colormap name used to map scalar datato colors.

normstr or Normalize, optional

The normalization method used to scale scalar data to the [0, 1] rangebefore mapping to colors using cmap. By default, a linear scaling isused, mapping the lowest value to 0 and the highest to 1.

See Also

xarray.plot.pcolormeshReshaping and reorganizing data

If given, this can be one of the following:

• An instance of Normalize or one of its subclasses(see Colormap normalization).

• A scale name, i.e. one of "linear", "log", "symlog", "logit", etc. For alist of available scales, call matplotlib.scale.get_scale_names().In that case, a suitable Normalize subclass is dynamically generatedand instantiated.

vmin, vmaxfloat, optional

When using scalar data and no explicit norm, vmin and vmax definethe data range that the colormap covers. By default, the colormap coversthe complete value range of the supplied data. It is an error to usevmin/vmax when a norm instance is given (but using a str normname together with vmin/vmax is acceptable).

edgecolors{'none', None, 'face', color, color sequence}, optional

The color of the edges. Defaults to 'none'. Possible values:

• 'none' or '': No edge.

• None: rcParams["patch.edgecolor"] (default: 'black') will be used. Note that currentlyrcParams["patch.force_edgecolor"] (default: False) has to be True for this to work.

• 'face': Use the adjacent face color.

• A color or sequence of colors will set the edge color.

The singular form edgecolor works as an alias.

alphafloat, default: None

The alpha blending value, between 0 (transparent) and 1 (opaque).

shading{'flat', 'nearest', 'gouraud', 'auto'}, optional

The fill style for the quadrilateral; defaults torcParams["pcolor.shading"] (default: 'auto'). Possible values:

• 'flat': A solid color is used for each quad. The color of thequad (i, j), (i+1, j), (i, j+1), (i+1, j+1) is given byC[i, j]. The dimensions of X and Y should beone greater than those of C; if they are the same as C,then a deprecation warning is raised, and the last rowand column of C are dropped.

• 'nearest': Each grid point will have a color centered on it,extending halfway between the adjacent grid centers. Thedimensions of X and Y must be the same as C.

• 'gouraud': Each quad will be Gouraud shaded: The color of thecorners (i', j') are given by C[i', j']. The color values ofthe area in between is interpolated from the corner values.The dimensions of X and Y must be the same as C. WhenGouraud shading is used, edgecolors is ignored.

• 'auto': Choose 'flat' if dimensions of X and Y are onelarger than C. Choose 'nearest' if dimensions are the same.

See pcolormesh grids and shadingfor more description.

snapbool, default: False

Whether to snap the mesh to pixel boundaries.

rasterizedbool, optional

Rasterize the pcolormesh when drawing vector graphics. This canspeed up rendering and produce smaller files for large data sets.See also Rasterization for vector graphics.

Returns:

matplotlib.collections.QuadMesh

Other Parameters:

dataindexable object, optional

If given, all parameters also accept a string s, which isinterpreted as data[s] (unless this raises an exception).

**kwargs

Additionally, the following arguments are allowed. They are passedalong to the QuadMesh constructor:

Property	Description
agg_filter	a filter function, which takes a (m, n, 3) float array and a dpi value, and returns a (m, n, 3) array and two offsets from the bottom left corner of the image
alpha	array-like or scalar or None
animated	bool
antialiased or aa or antialiaseds	bool or list of bools
array	array-like
capstyle	CapStyle or {'butt', 'projecting', 'round'}
clim	(vmin: float, vmax: float)
clip_box	BboxBase or None
clip_on	bool
clip_path	Patch or (Path, Transform) or None
cmap	Colormap or str or None
color	color or list of RGBA tuples
edgecolor or ec or edgecolors	color or list of color or 'face'
facecolor or facecolors or fc	color or list of color
figure	Figure
gid	str
hatch	{'/', '\', '|', '-', '+', 'x', 'o', 'O', '.', '*'}
in_layout	bool
joinstyle	JoinStyle or {'miter', 'round', 'bevel'}
label	object
linestyle or dashes or linestyles or ls	str or tuple or list thereof
linewidth or linewidths or lw	float or list of floats
mouseover	bool
norm	Normalize or str or None
offset_transform or transOffset	Transform
offsets	(N, 2) or (2,) array-like
path_effects	list of AbstractPathEffect
picker	None or bool or float or callable
pickradius	float
rasterized	bool
sketch_params	(scale: float, length: float, randomness: float)
snap	bool or None
transform	Transform
url	str
urls	list of str or None
visible	bool
zorder	float

Notes

Masked arrays

C may be a masked array. If C[i, j] is masked, the correspondingquadrilateral will be transparent. Masking of X and Y is notsupported. Use pcolor if you need this functionality.

Grid orientation

The grid orientation follows the standard matrix convention: An arrayC with shape (nrows, ncolumns) is plotted with the column number asX and the row number as Y.

Differences between pcolor() and pcolormesh()

Both methods are used to create a pseudocolor plot of a 2D arrayusing quadrilaterals.

The main difference lies in the created object and internal datahandling:While pcolor returns a PolyQuadMesh, pcolormeshreturns a QuadMesh. The latter is more specialized for the givenpurpose and thus is faster. It should almost always be preferred.

There is also a slight difference in the handling of masked arrays.Both pcolor and pcolormesh support masked arraysfor C. However, only pcolor supports masked arrays for Xand Y. The reason lies in the internal handling of the masked values.pcolor leaves out the respective polygons from thePolyQuadMesh. pcolormesh sets the facecolor of the maskedelements to transparent. You can see the difference when usingedgecolors. While all edges are drawn irrespective of masking in aQuadMesh, the edge between two adjacent masked quadrilaterals inpcolor is not drawn as the corresponding polygons do notexist in the PolyQuadMesh. Because PolyQuadMesh draws each individualpolygon, it also supports applying hatches and linestyles to the collection.

Another difference is the support of Gouraud shading inpcolormesh, which is not available with pcolor.