Top-Level Chart Configuration

Many aspects of a chart’s appearance can be configured at the top level using the configure_*() methods. These methods and the properties that they set are only valid at the top level of a chart, and can be thought of as a way of setting a chart theme: that is, they set the default styles for the entire chart, and these defaults can be overridden by specific style settings associated with chart elements.

These methods and their arguments will be outlined below:

• Chart Configuration Chart.configure()

• Axis Configuration Chart.configure_axis()

• Header Configuration Chart.configure_header()

• Legend Configuration Chart.configure_legend()

• Mark and Mark Style Configuration Chart.configure_mark()

• Scale Configuration Chart.configure_scale()

• Scale Range Configuration Chart.configure_range()

• Projection Configuration Chart.configure_projection()

• Selection Configuration Chart.configure_selection()

• Title Configuration Chart.configure_title()

• View Configuration Chart.configure_view()

For more discussion of approaches to chart customization, see Customizing Visualizations.

Chart Configuration

The Chart.configure() method adds a Config instance to the chart, and has the following attributes:

Property	Type	Description
area	AreaConfig	Area-Specific Config
autosize	anyOf(AutosizeType, AutoSizeParams)	How the visualization size should be determined. If a string, should be one of "pad", "fit" or "none". Object values can additionally specify parameters for content sizing and automatic resizing. Default value: pad
axis	AxisConfig	Axis configuration, which determines default properties for all x and y axes. For a full list of axis configuration options, please see the corresponding section of the axis documentation.
axisBand	AxisConfig	Config for axes with “band” scales.
axisBottom	AxisConfig	Config for x-axis along the bottom edge of the chart.
axisDiscrete	AxisConfig	Config for axes with “point” or “band” scales.
axisLeft	AxisConfig	Config for y-axis along the left edge of the chart.
axisPoint	AxisConfig	Config for axes with “point” scales.
axisQuantitative	AxisConfig	Config for quantitative axes.
axisRight	AxisConfig	Config for y-axis along the right edge of the chart.
axisTemporal	AxisConfig	Config for temporal axes.
axisTop	AxisConfig	Config for x-axis along the top edge of the chart.
axisX	AxisConfig	X-axis specific config.
axisXBand	AxisConfig	Config for x-axes with “band” scales.
axisXDiscrete	AxisConfig	Config for x-axes with “point” or “band” scales.
axisXPoint	AxisConfig	Config for x-axes with “point” scales.
axisXQuantitative	AxisConfig	Config for x-quantitative axes.
axisXTemporal	AxisConfig	Config for x-temporal axes.
axisY	AxisConfig	Y-axis specific config.
axisYBand	AxisConfig	Config for y-axes with “band” scales.
axisYDiscrete	AxisConfig	Config for y-axes with “point” or “band” scales.
axisYPoint	AxisConfig	Config for y-axes with “point” scales.
axisYQuantitative	AxisConfig	Config for y-quantitative axes.
axisYTemporal	AxisConfig	Config for y-temporal axes.
background	Color	CSS color property to use as the background of the entire view. Default value: "white"
bar	BarConfig	Bar-Specific Config
boxplot	BoxPlotConfig	Box Config
circle	MarkConfig	Circle-Specific Config
concat	CompositionConfig	Default configuration for all concatenation and repeat view composition operators (concat, hconcat, vconcat, and repeat)
countTitle	string	Default axis and legend title for count fields. Default value: 'Count of Records.
errorband	ErrorBandConfig	ErrorBand Config
errorbar	ErrorBarConfig	ErrorBar Config
facet	CompositionConfig	Default configuration for the facet view composition operator
fieldTitle	[‘verbal’, ‘functional’, ‘plain’]	Defines how Vega-Lite generates title for fields. There are three possible styles: "verbal" (Default) - displays function in a verbal style (e.g., “Sum of field”, “Year-month of date”, “field (binned)”). "function" - displays function using parentheses and capitalized texts (e.g., “SUM(field)”, “YEARMONTH(date)”, “BIN(field)”). "plain" - displays only the field name without functions (e.g., “field”, “date”, “field”).
font	string	Default font for all text marks, titles, and labels.
geoshape	MarkConfig	Geoshape-Specific Config
header	HeaderConfig	Header configuration, which determines default properties for all headers. For a full list of header configuration options, please see the corresponding section of in the header documentation.
headerColumn	HeaderConfig	Header configuration, which determines default properties for column headers. For a full list of header configuration options, please see the corresponding section of in the header documentation.
headerFacet	HeaderConfig	Header configuration, which determines default properties for non-row/column facet headers. For a full list of header configuration options, please see the corresponding section of in the header documentation.
headerRow	HeaderConfig	Header configuration, which determines default properties for row headers. For a full list of header configuration options, please see the corresponding section of in the header documentation.
image	RectConfig	Image-specific Config
legend	LegendConfig	Legend configuration, which determines default properties for all legends. For a full list of legend configuration options, please see the corresponding section of in the legend documentation.
line	LineConfig	Line-Specific Config
lineBreak	string	A delimiter, such as a newline character, upon which to break text strings into multiple lines. This property provides a global default for text marks, which is overridden by mark or style config settings, and by the lineBreak mark encoding channel. If signal-valued, either string or regular expression (regexp) values are valid.
mark	MarkConfig	Mark Config
numberFormat	string	D3 Number format for guide labels and text marks. For example "s" for SI units. Use D3’s number format pattern.
padding	Padding	The default visualization padding, in pixels, from the edge of the visualization canvas to the data rectangle. If a number, specifies padding for all sides. If an object, the value should have the format {"left": 5, "top": 5, "right": 5, "bottom": 5} to specify padding for each side of the visualization. Default value: 5
point	MarkConfig	Point-Specific Config
projection	ProjectionConfig	Projection configuration, which determines default properties for all projections. For a full list of projection configuration options, please see the corresponding section of the projection documentation.
range	RangeConfig	An object hash that defines default range arrays or schemes for using with scales. For a full list of scale range configuration options, please see the corresponding section of the scale documentation.
rect	RectConfig	Rect-Specific Config
rule	MarkConfig	Rule-Specific Config
scale	ScaleConfig	Scale configuration determines default properties for all scales. For a full list of scale configuration options, please see the corresponding section of the scale documentation.
selection	SelectionConfig	An object hash for defining default properties for each type of selections.
square	MarkConfig	Square-Specific Config
style	StyleConfigIndex	An object hash that defines key-value mappings to determine default properties for marks with a given style. The keys represent styles names; the values have to be valid mark configuration objects.
text	MarkConfig	Text-Specific Config
tick	TickConfig	Tick-Specific Config
timeFormat	string	Default time format for raw time values (without time units) in text marks, legend labels and header labels. Default value: "%b %d, %Y" Note: Axes automatically determine the format for each label automatically so this config does not affect axes.
title	TitleConfig	Title configuration, which determines default properties for all titles. For a full list of title configuration options, please see the corresponding section of the title documentation.
trail	LineConfig	Trail-Specific Config
view	ViewConfig	Default properties for single view plots.

Axis Configuration

Axis configuration defines default settings for axes, and can be set using the Chart.configure_axis() method. Properties defined here are applied to all axes in the figure.

Additional property blocks can target more specific axis types based on the orientation (“axisX”, “axisY”, “axisLeft”, “axisTop”, etc.) or band scale type (“axisBand”). For example, properties defined under the “axisBand” property will only apply to axes visualizing “band” scales. If multiple axis config blocks apply to a single axis, type-based options take precedence over orientation-based options, which in turn take precedence over general options.

The methods are the following:

• Chart.configure_axis()

• Chart.configure_axisBand()

• Chart.configure_axisBottom()

• Chart.configure_axisLeft()

• Chart.configure_axisRight()

• Chart.configure_axisTop()

• Chart.configure_axisX()

• Chart.configure_axisY()

They have the following properties:

Property	Type	Description
bandPosition	number	An interpolation fraction indicating where, for band scales, axis ticks should be positioned. A value of 0 places ticks at the left edge of their bands. A value of 0.5 places ticks in the middle of their bands. Default value: 0.5
disable	boolean	Disable axis by default.
domain	boolean	A boolean flag indicating if the domain (the axis baseline) should be included as part of the axis. Default value: true
domainColor	anyOf(null, Color)	Color of axis domain line. Default value: "gray".
domainDash	array(number)	An array of alternating [stroke, space] lengths for dashed domain lines.
domainDashOffset	number	The pixel offset at which to start drawing with the domain dash array.
domainOpacity	number	Opacity of the axis domain line.
domainWidth	number	Stroke width of axis domain line Default value: 1
grid	boolean	A boolean flag indicating if grid lines should be included as part of the axis Default value: true for continuous scales that are not binned; otherwise, false.
gridColor	anyOf(anyOf(null, Color), ConditionalAxisColor)
gridDash	anyOf(array(number), ConditionalAxisNumberArray)
gridDashOffset	anyOf(number, ConditionalAxisNumber)
gridOpacity	anyOf(number, ConditionalAxisNumber)
gridWidth	anyOf(number, ConditionalAxisNumber)
labelAlign	anyOf(Align, ConditionalAxisLabelAlign)
labelAngle	number	The rotation angle of the axis labels. Default value: -90 for nominal and ordinal fields; 0 otherwise.
labelBaseline	anyOf(TextBaseline, ConditionalAxisLabelBaseline)
labelBound	[number, boolean]	Indicates if labels should be hidden if they exceed the axis range. If false (the default) no bounds overlap analysis is performed. If true, labels will be hidden if they exceed the axis range by more than 1 pixel. If this property is a number, it specifies the pixel tolerance: the maximum amount by which a label bounding box may exceed the axis range. Default value: false.
labelColor	anyOf(anyOf(null, Color), ConditionalAxisColor)
labelExpr	string	Vega expression for customizing labels. Note: The label text and value can be assessed via the label and value properties of the axis’s backing datum object.
labelFlush	[boolean, number]	Indicates if the first and last axis labels should be aligned flush with the scale range. Flush alignment for a horizontal axis will left-align the first label and right-align the last label. For vertical axes, bottom and top text baselines are applied instead. If this property is a number, it also indicates the number of pixels by which to offset the first and last labels; for example, a value of 2 will flush-align the first and last labels and also push them 2 pixels outward from the center of the axis. The additional adjustment can sometimes help the labels better visually group with corresponding axis ticks. Default value: true for axis of a continuous x-scale. Otherwise, false.
labelFlushOffset	number	Indicates the number of pixels by which to offset flush-adjusted labels. For example, a value of 2 will push flush-adjusted labels 2 pixels outward from the center of the axis. Offsets can help the labels better visually group with corresponding axis ticks. Default value: 0.
labelFont	anyOf(string, ConditionalAxisString)
labelFontSize	anyOf(number, ConditionalAxisNumber)
labelFontStyle	anyOf(FontStyle, ConditionalAxisLabelFontStyle)
labelFontWeight	anyOf(FontWeight, ConditionalAxisLabelFontWeight)
labelLimit	number	Maximum allowed pixel width of axis tick labels. Default value: 180
labelLineHeight	number	Line height in pixels for multi-line label text.
labelOffset	anyOf(number, ConditionalAxisNumber)
labelOpacity	anyOf(number, ConditionalAxisNumber)
labelOverlap	LabelOverlap	The strategy to use for resolving overlap of axis labels. If false (the default), no overlap reduction is attempted. If set to true or "parity", a strategy of removing every other label is used (this works well for standard linear axes). If set to "greedy", a linear scan of the labels is performed, removing any labels that overlaps with the last visible label (this often works better for log-scaled axes). Default value: true for non-nominal fields with non-log scales; "greedy" for log scales; otherwise false.
labelPadding	anyOf(number, ConditionalAxisNumber)
labelSeparation	number	The minimum separation that must be between label bounding boxes for them to be considered non-overlapping (default 0). This property is ignored if labelOverlap resolution is not enabled.
labels	boolean	A boolean flag indicating if labels should be included as part of the axis. Default value: true.
maxExtent	number	The maximum extent in pixels that axis ticks and labels should use. This determines a maximum offset value for axis titles. Default value: undefined.
minExtent	number	The minimum extent in pixels that axis ticks and labels should use. This determines a minimum offset value for axis titles. Default value: 30 for y-axis; undefined for x-axis.
offset	number	The offset, in pixels, by which to displace the axis from the edge of the enclosing group or data rectangle. Default value: derived from the axis config’s offset (0 by default)
orient	AxisOrient	The orientation of the axis. One of "top", "bottom", "left" or "right". The orientation can be used to further specialize the axis type (e.g., a y-axis oriented towards the right edge of the chart). Default value: "bottom" for x-axes and "left" for y-axes.
style	anyOf(string, array(string))	A string or array of strings indicating the name of custom styles to apply to the axis. A style is a named collection of axis property defined within the style configuration. If style is an array, later styles will override earlier styles. Default value: (none) Note: Any specified style will augment the default style. For example, an x-axis mark with "style": "foo" will use config.axisX and config.style.foo (the specified style "foo" has higher precedence).
tickBand	[‘center’, ‘extent’]	For band scales, indicates if ticks and grid lines should be placed at the center of a band (default) or at the band extents to indicate intervals.
tickColor	anyOf(anyOf(null, Color), ConditionalAxisColor)
tickCount	number	A desired number of ticks, for axes visualizing quantitative scales. The resulting number may be different so that values are “nice” (multiples of 2, 5, 10) and lie within the underlying scale’s range. Default value: Determine using a formula ceil(width/40) for x and ceil(height/40) for y.
tickDash	anyOf(array(number), ConditionalAxisNumberArray)
tickDashOffset	anyOf(number, ConditionalAxisNumber)
tickExtra	boolean	Boolean flag indicating if an extra axis tick should be added for the initial position of the axis. This flag is useful for styling axes for band scales such that ticks are placed on band boundaries rather in the middle of a band. Use in conjunction with "bandPosition": 1 and an axis "padding" value of 0.
tickOffset	number	Position offset in pixels to apply to ticks, labels, and gridlines.
tickOpacity	anyOf(number, ConditionalAxisNumber)
tickRound	boolean	Boolean flag indicating if pixel position values should be rounded to the nearest integer. Default value: true
tickSize	anyOf(number, ConditionalAxisNumber)
tickWidth	anyOf(number, ConditionalAxisNumber)
ticks	boolean	Boolean value that determines whether the axis should include ticks. Default value: true
title	null	Set to null to disable title for the axis, legend, or header.
titleAlign	Align	Horizontal text alignment of axis titles.
titleAnchor	TitleAnchor	Text anchor position for placing axis titles.
titleAngle	number	Angle in degrees of axis titles.
titleBaseline	TextBaseline	Vertical text baseline for axis titles.
titleColor	anyOf(null, Color)	Color of the title, can be in hex color code or regular color name.
titleFont	string	Font of the title. (e.g., "Helvetica Neue").
titleFontSize	number	Font size of the title.
titleFontStyle	FontStyle	Font style of the title.
titleFontWeight	FontWeight	Font weight of the title. This can be either a string (e.g "bold", "normal") or a number (100, 200, 300, …, 900 where "normal" = 400 and "bold" = 700).
titleLimit	number	Maximum allowed pixel width of axis titles.
titleLineHeight	number	Line height in pixels for multi-line title text.
titleOpacity	number	Opacity of the axis title.
titlePadding	number	The padding, in pixels, between title and axis.
titleX	number	X-coordinate of the axis title relative to the axis group.
titleY	number	Y-coordinate of the axis title relative to the axis group.
translate	number	Translation offset in pixels applied to the axis group mark x and y. If specified, overrides the default behavior of a 0.5 offset to pixel-align stroked lines.

Header Configuration

The Chart.configure_header() method allows configuration of facet headers, including the font, color, size, and position of the title and labels. Here is an example:

import altair as alt
from vega_datasets import data

source = data.cars.url

chart = alt.Chart(source).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color='Origin:N',
    column='Origin:N'
).properties(
    width=180,
    height=180
)

chart.configure_header(
    titleColor='green',
    titleFontSize=14,
    labelColor='red',
    labelFontSize=14
)

Property	Type	Description
format	anyOf(string, dict)	When used with the default "number" and "time" format type, the text formatting pattern for labels of guides (axes, legends, headers) and text marks. If the format type is "number" (e.g., for quantitative fields), this is D3’s number format pattern. If the format type is "time" (e.g., for temporal fields), this is D3’s time format pattern. See the format documentation for more examples. When used with a custom "formatType" that takes datum.value and format parameter as input), this property represents the format parameter. Default value: Derived from numberFormat config for number format and from timeFormat config for time format.
formatType	string	The format type for labels ("number" or "time" or a registered custom format type). Default value: "time" for temporal fields and ordinal and nomimal fields with timeUnit. "number" for quantitative fields as well as ordinal and nomimal fields without timeUnit.
labelAlign	Align	Horizontal text alignment of header labels. One of "left", "center", or "right".
labelAnchor	TitleAnchor	The anchor position for placing the labels. One of "start", "middle", or "end". For example, with a label orientation of top these anchor positions map to a left-, center-, or right-aligned label.
labelAngle	number	The rotation angle of the header labels. Default value: 0 for column header, -90 for row header.
labelBaseline	TextBaseline	The vertical text baseline for the header labels. One of "alphabetic" (default), "top", "middle", "bottom", "line-top", or "line-bottom". The "line-top" and "line-bottom" values operate similarly to "top" and "bottom", but are calculated relative to the titleLineHeight rather than titleFontSize alone.
labelColor	Color	The color of the header label, can be in hex color code or regular color name.
labelExpr	string	Vega expression for customizing labels. Note: The label text and value can be assessed via the label and value properties of the header’s backing datum object.
labelFont	string	The font of the header label.
labelFontSize	number	The font size of the header label, in pixels.
labelFontStyle	FontStyle	The font style of the header label.
labelFontWeight	FontWeight	The font weight of the header label.
labelLimit	number	The maximum length of the header label in pixels. The text value will be automatically truncated if the rendered size exceeds the limit. Default value: 0, indicating no limit
labelLineHeight	number	Line height in pixels for multi-line header labels or title text with "line-top" or "line-bottom" baseline.
labelOrient	Orient	The orientation of the header label. One of "top", "bottom", "left" or "right".
labelPadding	number	The padding, in pixel, between facet header’s label and the plot. Default value: 10
labels	boolean	A boolean flag indicating if labels should be included as part of the header. Default value: true.
orient	Orient	Shortcut for setting both labelOrient and titleOrient.
title	null	Set to null to disable title for the axis, legend, or header.
titleAlign	Align	Horizontal text alignment (to the anchor) of header titles.
titleAnchor	TitleAnchor	The anchor position for placing the title. One of "start", "middle", or "end". For example, with an orientation of top these anchor positions map to a left-, center-, or right-aligned title.
titleAngle	number	The rotation angle of the header title. Default value: 0.
titleBaseline	TextBaseline	The vertical text baseline for the header title. One of "alphabetic" (default), "top", "middle", "bottom", "line-top", or "line-bottom". The "line-top" and "line-bottom" values operate similarly to "top" and "bottom", but are calculated relative to the titleLineHeight rather than titleFontSize alone. Default value: "middle"
titleColor	Color	Color of the header title, can be in hex color code or regular color name.
titleFont	string	Font of the header title. (e.g., "Helvetica Neue").
titleFontSize	number	Font size of the header title.
titleFontStyle	FontStyle	The font style of the header title.
titleFontWeight	FontWeight	Font weight of the header title. This can be either a string (e.g "bold", "normal") or a number (100, 200, 300, …, 900 where "normal" = 400 and "bold" = 700).
titleLimit	number	The maximum length of the header title in pixels. The text value will be automatically truncated if the rendered size exceeds the limit. Default value: 0, indicating no limit
titleLineHeight	number	Line height in pixels for multi-line header title text or title text with "line-top" or "line-bottom" baseline.
titleOrient	Orient	The orientation of the header title. One of "top", "bottom", "left" or "right".
titlePadding	number	The padding, in pixel, between facet header’s title and the label. Default value: 10

Legend Configuration

The Chart.configure_legend() allows you to customize the appearance of chart legends, including location, fonts, bounding boxes, colors, and more. Here is an example:

import altair as alt
from vega_datasets import data

source = data.cars.url

chart = alt.Chart(source).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color='Origin:N'
)

chart.configure_legend(
    strokeColor='gray',
    fillColor='#EEEEEE',
    padding=10,
    cornerRadius=10,
    orient='top-right'
)

Additional properties are summarized in the following table:

Property	Type	Description
clipHeight	number	The height in pixels to clip symbol legend entries and limit their size.
columnPadding	number	The horizontal padding in pixels between symbol legend entries. Default value: 10.
columns	number	The number of columns in which to arrange symbol legend entries. A value of 0 or lower indicates a single row with one column per entry.
cornerRadius	number	Corner radius for the full legend.
direction	Orientation	The direction of the legend, one of "vertical" or "horizontal". Default value: For top-/bottom-oriented legends, "horizontal" For left-/right-oriented legends, "vertical" For top/bottom-left/right-oriented legends, "horizontal" for gradient legends and "vertical" for symbol legends.
disable	boolean	Disable legend by default
fillColor	anyOf(null, Color)	Background fill color for the full legend.
gradientDirection	Orientation	The default direction ("horizontal" or "vertical") for gradient legends. Default value: "vertical".
gradientHorizontalMaxLength	number	Max legend length for a horizontal gradient when config.legend.gradientLength is undefined. Default value: 200
gradientHorizontalMinLength	number	Min legend length for a horizontal gradient when config.legend.gradientLength is undefined. Default value: 100
gradientLabelLimit	number	The maximum allowed length in pixels of color ramp gradient labels.
gradientLabelOffset	number	Vertical offset in pixels for color ramp gradient labels. Default value: 2.
gradientLength	number	The length in pixels of the primary axis of a color gradient. This value corresponds to the height of a vertical gradient or the width of a horizontal gradient. Default value: 200.
gradientOpacity	number	Opacity of the color gradient.
gradientStrokeColor	anyOf(null, Color)	The color of the gradient stroke, can be in hex color code or regular color name. Default value: "lightGray".
gradientStrokeWidth	number	The width of the gradient stroke, in pixels. Default value: 0.
gradientThickness	number	The thickness in pixels of the color gradient. This value corresponds to the width of a vertical gradient or the height of a horizontal gradient. Default value: 16.
gradientVerticalMaxLength	number	Max legend length for a vertical gradient when config.legend.gradientLength is undefined. Default value: 200
gradientVerticalMinLength	number	Min legend length for a vertical gradient when config.legend.gradientLength is undefined. Default value: 100
gridAlign	LayoutAlign	The alignment to apply to symbol legends rows and columns. The supported string values are "all", "each" (the default), and none. For more information, see the grid layout documentation. Default value: "each".
labelAlign	Align	The alignment of the legend label, can be left, center, or right.
labelBaseline	TextBaseline	The position of the baseline of legend label, can be "top", "middle", "bottom", or "alphabetic". Default value: "middle".
labelColor	anyOf(null, Color)	The color of the legend label, can be in hex color code or regular color name.
labelFont	string	The font of the legend label.
labelFontSize	number	The font size of legend label. Default value: 10.
labelFontStyle	FontStyle	The font style of legend label.
labelFontWeight	FontWeight	The font weight of legend label.
labelLimit	number	Maximum allowed pixel width of legend tick labels. Default value: 160.
labelOffset	number	The offset of the legend label.
labelOpacity	number	Opacity of labels.
labelOverlap	LabelOverlap	The strategy to use for resolving overlap of labels in gradient legends. If false, no overlap reduction is attempted. If set to true or "parity", a strategy of removing every other label is used. If set to "greedy", a linear scan of the labels is performed, removing any label that overlaps with the last visible label (this often works better for log-scaled axes). Default value: "greedy" for log scales otherwise true`.
labelPadding	number	Padding in pixels between the legend and legend labels.
labelSeparation	number	The minimum separation that must be between label bounding boxes for them to be considered non-overlapping (default 0). This property is ignored if labelOverlap resolution is not enabled.
layout	–	Legend orient group layout parameters.
legendX	number	Custom x-position for legend with orient “none”.
legendY	number	Custom y-position for legend with orient “none”.
offset	number	The offset in pixels by which to displace the legend from the data rectangle and axes. Default value: 18.
orient	LegendOrient	The orientation of the legend, which determines how the legend is positioned within the scene. One of "left", "right", "top", "bottom", "top-left", "top-right", "bottom-left", "bottom-right", "none". Default value: "right"
padding	number	The padding between the border and content of the legend group. Default value: 0.
rowPadding	number	The vertical padding in pixels between symbol legend entries. Default value: 2.
strokeColor	anyOf(null, Color)	Border stroke color for the full legend.
strokeDash	array(number)	Border stroke dash pattern for the full legend.
strokeWidth	number	Border stroke width for the full legend.
symbolBaseFillColor	anyOf(null, Color)	Default fill color for legend symbols. Only applied if there is no "fill" scale color encoding for the legend. Default value: "transparent".
symbolBaseStrokeColor	anyOf(null, Color)	Default stroke color for legend symbols. Only applied if there is no "fill" scale color encoding for the legend. Default value: "gray".
symbolDash	array(number)	An array of alternating [stroke, space] lengths for dashed symbol strokes.
symbolDashOffset	number	The pixel offset at which to start drawing with the symbol stroke dash array.
symbolDirection	Orientation	The default direction ("horizontal" or "vertical") for symbol legends. Default value: "vertical".
symbolFillColor	anyOf(null, Color)	The color of the legend symbol,
symbolLimit	number	The maximum number of allowed entries for a symbol legend. Additional entries will be dropped.
symbolOffset	number	Horizontal pixel offset for legend symbols. Default value: 0.
symbolOpacity	number	Opacity of the legend symbols.
symbolSize	number	The size of the legend symbol, in pixels. Default value: 100.
symbolStrokeColor	anyOf(null, Color)	Stroke color for legend symbols.
symbolStrokeWidth	number	The width of the symbol’s stroke. Default value: 1.5.
symbolType	SymbolShape	The symbol shape. One of the plotting shapes circle (default), square, cross, diamond, triangle-up, triangle-down, triangle-right, or triangle-left, the line symbol stroke, or one of the centered directional shapes arrow, wedge, or triangle. Alternatively, a custom SVG path string can be provided. For correct sizing, custom shape paths should be defined within a square bounding box with coordinates ranging from -1 to 1 along both the x and y dimensions. Default value: "circle".
tickCount	TickCount	The desired number of tick values for quantitative legends.
title	null	Set to null to disable title for the axis, legend, or header.
titleAlign	Align	Horizontal text alignment for legend titles. Default value: "left".
titleAnchor	TitleAnchor	Text anchor position for placing legend titles.
titleBaseline	TextBaseline	Vertical text baseline for legend titles. Default value: "top".
titleColor	anyOf(null, Color)	The color of the legend title, can be in hex color code or regular color name.
titleFont	string	The font of the legend title.
titleFontSize	number	The font size of the legend title.
titleFontStyle	FontStyle	The font style of the legend title.
titleFontWeight	FontWeight	The font weight of the legend title. This can be either a string (e.g "bold", "normal") or a number (100, 200, 300, …, 900 where "normal" = 400 and "bold" = 700).
titleLimit	number	Maximum allowed pixel width of legend titles. Default value: 180.
titleLineHeight	number	Line height in pixels for multi-line title text.
titleOpacity	number	Opacity of the legend title.
titleOrient	Orient	Orientation of the legend title.
titlePadding	number	The padding, in pixels, between title and legend. Default value: 5.
unselectedOpacity	number	The opacity of unselected legend entries. Default value: 0.35.

Mark and Mark Style Configuration

The mark configuration can be set using the Chart.configure_mark() method, which sets the default properties for all marks in the chart. In addition, the config object also provides mark-specific configuration using the mark type (e.g. Chart.configure_area()) for defining default properties for each mark.

For general configuration of all mark types, use:

• Chart.configure_mark()

For configurations specific to particular mark types, use:

• Chart.configure_area()

• Chart.configure_bar()

• Chart.configure_circle()

• Chart.configure_geoshape()

• Chart.configure_line()

• Chart.configure_point()

• Chart.configure_rect()

• Chart.configure_rule()

• Chart.configure_square()

• Chart.configure_text()

• Chart.configure_tick()

• Chart.configure_trail()

Each of the above methods accepts the following properties:

Property	Type	Description
align	Align	The horizontal alignment of the text or ranged marks (area, bar, image, rect, rule). One of "left", "right", "center".
angle	number	The rotation angle of the text, in degrees.
aspect	boolean	Whether to keep aspect ratio of image marks.
baseline	TextBaseline	The vertical text baseline. One of "alphabetic" (default), "top", "middle", "bottom", "line-top", or "line-bottom". The "line-top" and "line-bottom" values operate similarly to "top" and "bottom", but are calculated relative to the lineHeight rather than fontSize alone.
blend	Blend	The color blend mode for drawing an item on its current background. Any valid CSS mix-blend-mode value can be used. __Default value: "source-over"
color	anyOf(Color, Gradient)	Default color. Default value: ■ "#4682b4" Note: This property cannot be used in a style config. The fill and stroke properties have higher precedence than color and will override color.
cornerRadius	number	The radius in pixels of rounded rectangle corners. Default value: 0
cornerRadiusBottomLeft	number	The radius in pixels of rounded rectangle bottom left corner. Default value: 0
cornerRadiusBottomRight	number	The radius in pixels of rounded rectangle bottom right corner. Default value: 0
cornerRadiusTopLeft	number	The radius in pixels of rounded rectangle top right corner. Default value: 0
cornerRadiusTopRight	number	The radius in pixels of rounded rectangle top left corner. Default value: 0
cursor	Cursor	The mouse cursor used over the mark. Any valid CSS cursor type can be used.
dir	TextDirection	The direction of the text. One of "ltr" (left-to-right) or "rtl" (right-to-left). This property determines on which side is truncated in response to the limit parameter. Default value: "ltr"
dx	number	The horizontal offset, in pixels, between the text label and its anchor point. The offset is applied after rotation by the angle property.
dy	number	The vertical offset, in pixels, between the text label and its anchor point. The offset is applied after rotation by the angle property.
ellipsis	string	The ellipsis string for text truncated in response to the limit parameter. Default value: "…"
fill	anyOf(Color, Gradient, null)	Default Fill Color. This property has higher precedence than config.color. Default value: (None)
fillOpacity	number	The fill opacity (value between [0,1]). Default value: 1
filled	boolean	Whether the mark’s color should be used as fill color instead of stroke color. Default value: false for all point, line, and rule marks as well as geoshape marks for graticule data sources; otherwise, true. Note: This property cannot be used in a style config.
font	string	The typeface to set the text in (e.g., "Helvetica Neue").
fontSize	number	The font size, in pixels. Default value: 11
fontStyle	FontStyle	The font style (e.g., "italic").
fontWeight	FontWeight	The font weight. This can be either a string (e.g "bold", "normal") or a number (100, 200, 300, …, 900 where "normal" = 400 and "bold" = 700).
height	number	Height of the marks.
href	string	A URL to load upon mouse click. If defined, the mark acts as a hyperlink.
interpolate	Interpolate	The line interpolation method to use for line and area marks. One of the following: "linear": piecewise linear segments, as in a polyline. "linear-closed": close the linear segments to form a polygon. "step": alternate between horizontal and vertical segments, as in a step function. "step-before": alternate between vertical and horizontal segments, as in a step function. "step-after": alternate between horizontal and vertical segments, as in a step function. "basis": a B-spline, with control point duplication on the ends. "basis-open": an open B-spline; may not intersect the start or end. "basis-closed": a closed B-spline, as in a loop. "cardinal": a Cardinal spline, with control point duplication on the ends. "cardinal-open": an open Cardinal spline; may not intersect the start or end, but will intersect other control points. "cardinal-closed": a closed Cardinal spline, as in a loop. "bundle": equivalent to basis, except the tension parameter is used to straighten the spline. "monotone": cubic interpolation that preserves monotonicity in y.
invalid	[‘filter’, None]	Defines how Vega-Lite should handle marks for invalid values (null and NaN). If set to "filter" (default), all data items with null values will be skipped (for line, trail, and area marks) or filtered (for other marks). If null, all data items are included. In this case, invalid values will be interpreted as zeroes.
limit	number	The maximum length of the text mark in pixels. The text value will be automatically truncated if the rendered size exceeds the limit. Default value: 0 – indicating no limit
lineBreak	string	A delimiter, such as a newline character, upon which to break text strings into multiple lines. This property is ignored if the text is array-valued.
lineHeight	number	The line height in pixels (the spacing between subsequent lines of text) for multi-line text marks.
opacity	number	The overall opacity (value between [0,1]). Default value: 0.7 for non-aggregate plots with point, tick, circle, or square marks or layered bar charts and 1 otherwise.
order	[null, boolean]	For line and trail marks, this order property can be set to null or false to make the lines use the original order in the data sources.
orient	Orientation	The orientation of a non-stacked bar, tick, area, and line charts. The value is either horizontal (default) or vertical. For bar, rule and tick, this determines whether the size of the bar and tick should be applied to x or y dimension. For area, this property determines the orient property of the Vega output. For line and trail marks, this property determines the sort order of the points in the line if config.sortLineBy is not specified. For stacked charts, this is always determined by the orientation of the stack; therefore explicitly specified value will be ignored.
radius	number	Polar coordinate radial offset, in pixels, of the text label from the origin determined by the x and y properties.
shape	anyOf(SymbolShape, string)	Shape of the point marks. Supported values include: plotting shapes: "circle", "square", "cross", "diamond", "triangle-up", "triangle-down", "triangle-right", or "triangle-left". the line symbol "stroke" centered directional shapes "arrow", "wedge", or "triangle" a custom SVG path string (For correct sizing, custom shape paths should be defined within a square bounding box with coordinates ranging from -1 to 1 along both the x and y dimensions.) Default value: "circle"
size	number	Default size for marks. For point/circle/square, this represents the pixel area of the marks. Note that this value sets the area of the symbol; the side lengths will increase with the square root of this value. For bar, this represents the band size of the bar, in pixels. For text, this represents the font size, in pixels. Default value: 30 for point, circle, square marks; width/height’s step 2 for bar marks with discrete dimensions; 5 for bar marks with continuous dimensions; 11 for text marks.
stroke	anyOf(Color, Gradient, null)	Default Stroke Color. This property has higher precedence than config.color. Default value: (None)
strokeCap	string	The stroke cap for line ending style. One of "butt", "round", or "square". Default value: "butt"
strokeDash	array(number)	An array of alternating stroke, space lengths for creating dashed or dotted lines.
strokeDashOffset	number	The offset (in pixels) into which to begin drawing with the stroke dash array.
strokeJoin	string	The stroke line join method. One of "miter", "round" or "bevel". Default value: "miter"
strokeMiterLimit	number	The miter limit at which to bevel a line join.
strokeOffset	number	The offset in pixels at which to draw the group stroke and fill. If unspecified, the default behavior is to dynamically offset stroked groups such that 1 pixel stroke widths align with the pixel grid.
strokeOpacity	number	The stroke opacity (value between [0,1]). Default value: 1
strokeWidth	number	The stroke width, in pixels.
tension	number	Depending on the interpolation type, sets the tension parameter (for line and area marks).
text	Text	Placeholder text if the text channel is not specified
theta	number	Polar coordinate angle, in radians, of the text label from the origin determined by the x and y properties. Values for theta follow the same convention of arc mark startAngle and endAngle properties: angles are measured in radians, with 0 indicating “north”.
timeUnitBand	number	Default relative band size for a time unit. If set to 1, the bandwidth of the marks will be equal to the time unit band step. If set to 0.5, bandwidth of the marks will be half of the time unit band step.
timeUnitBandPosition	number	Default relative band position for a time unit. If set to 0, the marks will be positioned at the beginning of the time unit band step. If set to 0.5, the marks will be positioned in the middle of the time unit band step.
tooltip	anyOf(number, string, boolean, TooltipContent, null)	The tooltip text string to show upon mouse hover or an object defining which fields should the tooltip be derived from. If tooltip is true or {"content": "encoding"}, then all fields from encoding will be used. If tooltip is {"content": "data"}, then all fields that appear in the highlighted data point will be used. If set to null or false, then no tooltip will be used. See the tooltip documentation for a detailed discussion about tooltip in Vega-Lite. Default value: null
width	number	Width of the marks.
x	anyOf(number, [‘width’])	X coordinates of the marks, or width of horizontal "bar" and "area" without specified x2 or width. The value of this channel can be a number or a string "width" for the width of the plot.
x2	anyOf(number, [‘width’])	X2 coordinates for ranged "area", "bar", "rect", and "rule". The value of this channel can be a number or a string "width" for the width of the plot.
y	anyOf(number, [‘height’])	Y coordinates of the marks, or height of vertical "bar" and "area" without specified y2 or height. The value of this channel can be a number or a string "height" for the height of the plot.
y2	anyOf(number, [‘height’])	Y2 coordinates for ranged "area", "bar", "rect", and "rule". The value of this channel can be a number or a string "height" for the height of the plot.

In addition to the default mark properties above, default values can be further customized using named styles defined as keyword arguments to the Chart.configure_style() method. Styles can then be invoked by including a style property within a mark definition object.

Scale Configuration

Scales can be configured using Chart.configure_scale(), which has the following properties:

Property	Type	Description
bandPaddingInner	number	Default inner padding for x and y band-ordinal scales. Default value: barBandPaddingInner for bar marks (0.1 by default) rectBandPaddingInner for rect and other marks (0 by default)
bandPaddingOuter	number	Default outer padding for x and y band-ordinal scales. Default value: paddingInner/2 (which makes width/height = number of unique values * step)
barBandPaddingInner	number	Default inner padding for x and y band-ordinal scales of "bar" marks. Default value: 0.1
clamp	boolean	If true, values that exceed the data domain are clamped to either the minimum or maximum range value
continuousPadding	number	Default padding for continuous scales. Default: 5 for continuous x-scale of a vertical bar and continuous y-scale of a horizontal bar.; 0 otherwise.
maxBandSize	number	The default max value for mapping quantitative fields to bar’s size/bandSize. If undefined (default), we will use the axis’s size (width or height) - 1.
maxFontSize	number	The default max value for mapping quantitative fields to text’s size/fontSize. Default value: 40
maxOpacity	number	Default max opacity for mapping a field to opacity. Default value: 0.8
maxSize	number	Default max value for point size scale.
maxStrokeWidth	number	Default max strokeWidth for the scale of strokeWidth for rule and line marks and of size for trail marks. Default value: 4
minBandSize	number	The default min value for mapping quantitative fields to bar and tick’s size/bandSize scale with zero=false. Default value: 2
minFontSize	number	The default min value for mapping quantitative fields to tick’s size/fontSize scale with zero=false Default value: 8
minOpacity	number	Default minimum opacity for mapping a field to opacity. Default value: 0.3
minSize	number	Default minimum value for point size scale with zero=false. Default value: 9
minStrokeWidth	number	Default minimum strokeWidth for the scale of strokeWidth for rule and line marks and of size for trail marks with zero=false. Default value: 1
pointPadding	number	Default outer padding for x and y point-ordinal scales. Default value: 0.5 (which makes width/height = number of unique values * step)
quantileCount	number	Default range cardinality for quantile scale. Default value: 4
quantizeCount	number	Default range cardinality for quantize scale. Default value: 4
rectBandPaddingInner	number	Default inner padding for x and y band-ordinal scales of "rect" marks. Default value: 0
round	boolean	If true, rounds numeric output values to integers. This can be helpful for snapping to the pixel grid. (Only available for x, y, and size scales.)
useUnaggregatedDomain	boolean	Use the source data range before aggregation as scale domain instead of aggregated data for aggregate axis. This is equivalent to setting domain to "unaggregate" for aggregated quantitative fields by default. This property only works with aggregate functions that produce values within the raw data domain ("mean", "average", "median", "q1", "q3", "min", "max"). For other aggregations that produce values outside of the raw data domain (e.g. "count", "sum"), this property is ignored. Default value: false
xReverse	boolean	Reverse x-scale by default (useful for right-to-left charts).

Scale Range Configuration

Scale ranges can be configured using Chart.configure_range(), which has the following properties:

Property	Type	Description
category	anyOf(RangeScheme, array(string))	Default color scheme for categorical data.
diverging	anyOf(RangeScheme, array(string))	Default color scheme for diverging quantitative ramps.
heatmap	anyOf(RangeScheme, array(string))	Default color scheme for quantitative heatmaps.
ordinal	anyOf(RangeScheme, array(string))	Default color scheme for rank-ordered data.
ramp	anyOf(RangeScheme, array(string))	Default color scheme for sequential quantitative ramps.
symbol	array(SymbolShape)	Array of symbol names or paths for the default shape palette.

Projection Configuration

Chart.configure_projection()

Property	Type	Description
center	Vector2<number>	The projection’s center, a two-element array of longitude and latitude in degrees. Default value: [0, 0]
clipAngle	number	The projection’s clipping circle radius to the specified angle in degrees. If null, switches to antimeridian cutting rather than small-circle clipping.
clipExtent	Vector2<Vector2<number>>	The projection’s viewport clip extent to the specified bounds in pixels. The extent bounds are specified as an array [[x0, y0], [x1, y1]], where x0 is the left-side of the viewport, y0 is the top, x1 is the right and y1 is the bottom. If null, no viewport clipping is performed.
coefficient	number
distance	number
extent	Vector2<Vector2<number>>
fit	anyOf(Fit, array(Fit))
fraction	number
lobes	number
parallel	number
parallels	array(number)	For conic projections, the two standard parallels that define the map layout. The default depends on the specific conic projection used.
pointRadius	number	The default radius (in pixels) to use when drawing GeoJSON Point and MultiPoint geometries. This parameter sets a constant default value. To modify the point radius in response to data, see the corresponding parameter of the GeoPath and GeoShape transforms. Default value: 4.5
precision	number	The threshold for the projection’s adaptive resampling to the specified value in pixels. This value corresponds to the Douglas–Peucker distance. If precision is not specified, returns the projection’s current resampling precision which defaults to √0.5 ≅ 0.70710….
radius	number
ratio	number
reflectX	boolean
reflectY	boolean
rotate	anyOf(Vector2<number>, Vector3<number>)	The projection’s three-axis rotation to the specified angles, which must be a two- or three-element array of numbers [lambda, phi, gamma] specifying the rotation angles in degrees about each spherical axis. (These correspond to yaw, pitch and roll.) Default value: [0, 0, 0]
scale	number	The projection’s scale (zoom) factor, overriding automatic fitting. The default scale is projection-specific. The scale factor corresponds linearly to the distance between projected points; however, scale factor values are not equivalent across projections.
size	Vector2<number>
spacing	number
tilt	number
translate	Vector2<number>	The projection’s translation offset as a two-element array [tx, ty].
type	ProjectionType	The cartographic projection to use. This value is case-insensitive, for example "albers" and "Albers" indicate the same projection type. You can find all valid projection types in the documentation. Default value: mercator

Selection Configuration

Chart.configure_selection()

Property	Type	Description
interval	IntervalSelectionConfig	The default definition for an interval selection. All properties and transformations for an interval selection definition (except type) may be specified here. For instance, setting interval to {"translate": false} disables the ability to move interval selections by default.
multi	MultiSelectionConfig	The default definition for a multi selection. All properties and transformations for a multi selection definition (except type) may be specified here. For instance, setting multi to {"toggle": "event.altKey"} adds additional values to multi selections when clicking with the alt-key pressed by default.
single	SingleSelectionConfig	The default definition for a single selection. All properties and transformations for a single selection definition (except type) may be specified here. For instance, setting single to {"on": "dblclick"} populates single selections on double-click by default.

Title Configuration

The Chart.configure_title() method allows configuration of the chart title, including the font, color, placement, and orientation. Here is an example:

import altair as alt
from vega_datasets import data

source = data.cars.url

chart = alt.Chart(source).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
).properties(
    title='Cars Data'
)

chart.configure_title(
    fontSize=20,
    font='Courier',
    anchor='start',
    color='gray'
)

Additional title configuration options are listed in the following table:

Property	Type	Description
align	Align	Horizontal text alignment for title text. One of "left", "center", or "right".
anchor	TitleAnchor	The anchor position for placing the title and subtitle text. One of "start", "middle", or "end". For example, with an orientation of top these anchor positions map to a left-, center-, or right-aligned title.
angle	number	Angle in degrees of title and subtitle text.
baseline	TextBaseline	Vertical text baseline for title and subtitle text. One of "top", "middle", "bottom", or "alphabetic".
color	anyOf(null, Color)	Text color for title text.
dx	number	Delta offset for title and subtitle text x-coordinate.
dy	number	Delta offset for title and subtitle text y-coordinate.
font	string	Font name for title text.
fontSize	number	Font size in pixels for title text.
fontStyle	FontStyle	Font style for title text.
fontWeight	FontWeight	Font weight for title text. This can be either a string (e.g "bold", "normal") or a number (100, 200, 300, …, 900 where "normal" = 400 and "bold" = 700).
frame	anyOf(TitleFrame, string)	The reference frame for the anchor position, one of "bounds" (to anchor relative to the full bounding box) or "group" (to anchor relative to the group width or height).
limit	number	The maximum allowed length in pixels of title and subtitle text.
lineHeight	number	Line height in pixels for multi-line title text.
offset	number	The orthogonal offset in pixels by which to displace the title group from its position along the edge of the chart.
orient	TitleOrient	Default title orientation ("top", "bottom", "left", or "right")
subtitleColor	anyOf(null, Color)	Text color for subtitle text.
subtitleFont	string	Font name for subtitle text.
subtitleFontSize	number	Font size in pixels for subtitle text.
subtitleFontStyle	FontStyle	Font style for subtitle text.
subtitleFontWeight	FontWeight	Font weight for subtitle text. This can be either a string (e.g "bold", "normal") or a number (100, 200, 300, …, 900 where "normal" = 400 and "bold" = 700).
subtitleLineHeight	number	Line height in pixels for multi-line subtitle text.
subtitlePadding	number	The padding in pixels between title and subtitle text.

View Configuration

The Chart.configure_view() method allows you to configure aspects of the chart’s view, i.e. the area of the screen in which the data and scales are drawn. Here is an example to demonstrate some of the visual features that can be controlled:

import altair as alt
from vega_datasets import data

source = data.cars.url

chart = alt.Chart(source).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
)

chart.configure_view(
    continuousHeight=200,
    continuousWidth=200,
    strokeWidth=4,
    fill='#FFEEDD',
    stroke='red',
)

Additional properties are summarized in the following table:

Property	Type	Description
clip	boolean	Whether the view should be clipped.
continuousHeight	number	The default height when the plot has a continuous y-field. Default value: 200
continuousWidth	number	The default width when the plot has a continuous x-field. Default value: 200
cornerRadius	number	The radius in pixels of rounded rectangle corners. Default value: 0
cursor	Cursor	The mouse cursor used over the view. Any valid CSS cursor type can be used.
discreteHeight	anyOf(number, dict)	The default height when the plot has either a discrete y-field or no y-field. The height can be either a number indicating a fixed height or an object in the form of {step: number} defining the height per discrete step. Default value: a step size based on config.view.step.
discreteWidth	anyOf(number, dict)	The default width when the plot has either a discrete x-field or no x-field. The width can be either a number indicating a fixed width or an object in the form of {step: number} defining the width per discrete step. Default value: a step size based on config.view.step.
fill	anyOf(Color, null)	The fill color. Default value: undefined
fillOpacity	number	The fill opacity (value between [0,1]). Default value: 1
height	number	Default height Deprecated: Since Vega-Lite 4.0. Please use continuousHeight and discreteHeight instead.
opacity	number	The overall opacity (value between [0,1]). Default value: 0.7 for non-aggregate plots with point, tick, circle, or square marks or layered bar charts and 1 otherwise.
step	number	Default step size for x-/y- discrete fields.
stroke	anyOf(Color, null)	The stroke color. Default value: "#ddd"
strokeCap	string	The stroke cap for line ending style. One of "butt", "round", or "square". Default value: "butt"
strokeDash	array(number)	An array of alternating stroke, space lengths for creating dashed or dotted lines.
strokeDashOffset	number	The offset (in pixels) into which to begin drawing with the stroke dash array.
strokeJoin	string	The stroke line join method. One of "miter", "round" or "bevel". Default value: "miter"
strokeMiterLimit	number	The miter limit at which to bevel a line join.
strokeOpacity	number	The stroke opacity (value between [0,1]). Default value: 1
strokeWidth	number	The stroke width, in pixels.
width	number	Default width Deprecated: Since Vega-Lite 4.0. Please use continuousWidth and discreteWidth instead.

Altair Themes

Altair makes available a theme registry that lets users apply chart configurations globally within any Python session. This is done via the alt.themes object.

The themes registry consists of functions which define a specification dictionary that will be added to every created chart. For example, the default theme configures the default size of a single chart:

>>> import altair as alt
>>> default = alt.themes.get()
>>> default()
{'config': {'view': {'continuousWidth': 400, 'continuousHeight': 300}}}

You can see that any chart you create will have this theme applied, and these configurations added to its specification:

import altair as alt
from vega_datasets import data

chart = alt.Chart(data.cars.url).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q'
)

chart.to_dict()

    {'config': {'view': {'continuousWidth': 400, 'continuousHeight': 300}}, 'data': {'url': 'https://vega.github.io/vega-datasets/data/cars.json'}, 'mark': 'point', 'encoding': {'x': {'type': 'quantitative', 'field': 'Horsepower'}, 'y': {'type': 'quantitative', 'field': 'Miles_per_Gallon'}}, '$schema': 'https://vega.github.io/schema/vega-lite/v4.8.1.json'}

The rendered chart will then reflect these configurations:

chart

Changing the Theme

If you would like to enable any other theme for the length of your Python session, you can call alt.themes.enable(theme_name). For example, Altair includes a theme in which the chart background is opaque rather than transparent:

alt.themes.enable('opaque')
chart.to_dict()

    {'config': {'background': 'white', 'view': {'continuousWidth': 400, 'continuousHeight': 300}}, 'data': {'url': 'https://vega.github.io/vega-datasets/data/cars.json'}, 'mark': 'point', 'encoding': {'x': {'type': 'quantitative', 'field': 'Horsepower'}, 'y': {'type': 'quantitative', 'field': 'Miles_per_Gallon'}}, '$schema': 'https://vega.github.io/schema/vega-lite/v4.8.1.json'}

chart

Notice that the background color of the chart is now set to white. If you would like no theme applied to your chart, you can use the theme named 'none':

alt.themes.enable('none')
chart.to_dict()

    {'data': {'url': 'https://vega.github.io/vega-datasets/data/cars.json'}, 'mark': 'point', 'encoding': {'x': {'type': 'quantitative', 'field': 'Horsepower'}, 'y': {'type': 'quantitative', 'field': 'Miles_per_Gallon'}}, '$schema': 'https://vega.github.io/schema/vega-lite/v4.8.1.json'}

chart

Because the view configuration is not set, the chart is smaller than the default rendering.

If you would like to use any theme just for a single chart, you can use the with statement to enable a temporary theme:

with alt.themes.enable('default'):
    spec = chart.to_json()

Currently Altair does not offer many built-in themes, but we plan to add more options in the future.

Defining a Custom Theme

The theme registry also allows defining and registering custom themes. A theme is simply a function that returns a dictionary of default values to be added to the chart specification at rendering time, which is then registered and activated.

For example, here we define a theme in which all marks are drawn with black fill unless otherwise specified:

import altair as alt
from vega_datasets import data

# define the theme by returning the dictionary of configurations
def black_marks():
    return {
        'config': {
            'view': {
                'height': 300,
                'width': 400,
            },
            'mark': {
                'color': 'black',
                'fill': 'black'
            }
        }
    }

# register the custom theme under a chosen name
alt.themes.register('black_marks', black_marks)

# enable the newly registered theme
alt.themes.enable('black_marks')

# draw the chart
cars = data.cars.url
alt.Chart(cars).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q'
)

If you want to restore the default theme, use:

alt.themes.enable('default')

For more ideas on themes, see the Vega Themes repository.