matplotlib.pyplot.pcolormesh

matplotlib.pyplot.pcolormesh(*args, alpha=None, norm=None, cmap=None, vmin=None, vmax=None, shading=None, antialiased=False, data=None, **kwargs)[source]

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.

Hint

pcolormesh is similar to pcolor. It is much faster and preferred in most cases. For a detailed discussion on the differences see Differences between pcolor() and pcolormesh().

Parameters
C2D array-like

The color-mapped values.

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, and the row index corresponds to y. For details, see the Notes section below.

If shading='flat' the dimensions of X and Y should be one greater than those of C, and the quadrilateral is colored due to the value at C[i, j]. If X, Y and C have equal dimensions, a warning will be raised and the last row and column of C will be ignored.

If shading='nearest' or 'gouraud', the dimensions of X and Y should be the same as those of C (if not, a ValueError will be raised). For 'nearest' the color C[i, j] is centered on (X[i, j], Y[i, j]). For 'gouraud', a smooth interpolation is caried out between the quadrilateral corners.

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

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

A Colormap instance or registered colormap name. The colormap maps the C values to colors.

normNormalize, optional

The Normalize instance scales the data values to the canonical colormap range [0, 1] for mapping to colors. By default, the data range is mapped to the colorbar range using linear scaling.

vmin, vmaxfloat, default: None

The colorbar range. If None, suitable min/max values are automatically chosen by the Normalize instance (defaults to the respective min/max values of C in case of the default linear scaling). It is an error to use vmin/vmax when norm is given.

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

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

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 to 'flat' or rcParams["pcolor.shading"] (default: 'auto'). Possible values:

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

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

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

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

See pcolormesh grids and shading for more description.

snapbool, default: False

Whether to snap the mesh to pixel boundaries.

rasterizedbool, optional

Rasterize the pcolormesh when drawing vector graphics. This can speed 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 is interpreted as data[s] (unless this raises an exception).

**kwargs

Additionally, the following arguments are allowed. They are passed along 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

alpha

array-like or scalar or None

animated

bool

antialiased or aa or antialiaseds

bool or list of bools

array

(M, N) array-like or M*N array-like

capstyle

CapStyle or {'butt', 'projecting', 'round'}

clim

(vmin: float, vmax: float)

clip_box

Bbox

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 colors or 'face'

facecolor or facecolors or fc

color or list of colors

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

norm

Normalize or None

offsets

(N, 2) or (2,) array-like

path_effects

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

See also

pcolor

An alternative implementation with slightly different features. For a detailed discussion on the differences see Differences between pcolor() and pcolormesh().

imshow

If X and Y are each equidistant, imshow can be a faster alternative.

Notes

Masked arrays

C may be a masked array. If C[i, j] is masked, the corresponding quadrilateral will be transparent. Masking of X and Y is not supported. Use pcolor if you need this functionality.

Grid orientation

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

Differences between pcolor() and pcolormesh()

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

The main difference lies in the created object and internal data handling: While pcolor returns a PolyCollection, pcolormesh returns a QuadMesh. The latter is more specialized for the given purpose 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 arrays for C. However, only pcolor supports masked arrays for X and Y. The reason lies in the internal handling of the masked values. pcolor leaves out the respective polygons from the PolyCollection. pcolormesh sets the facecolor of the masked elements to transparent. You can see the difference when using edgecolors. While all edges are drawn irrespective of masking in a QuadMesh, the edge between two adjacent masked quadrilaterals in pcolor is not drawn as the corresponding polygons do not exist in the PolyCollection.

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

Examples using matplotlib.pyplot.pcolormesh