Marks#

We saw in Encodings that the encode() method is used to map columns to visual attributes of the plot. The mark property is what specifies how exactly those attributes should be represented on the plot.

Altair supports the following primitive mark types:

Mark	Method	Description
Arc	`mark_arc()`	A pie chart.
Area	`mark_area()`	A filled area plot.
Bar	`mark_bar()`	A bar plot.
Circle	`mark_circle()`	A scatter plot with filled circles.
Geoshape	`mark_geoshape()`	Visualization containing spatial data
Image	`mark_image()`	A scatter plot with image markers.
Line	`mark_line()`	A line plot.
Point	`mark_point()`	A scatter plot with configurable point shapes.
Rect	`mark_rect()`	A filled rectangle, used for heatmaps
Rule	`mark_rule()`	A vertical or horizontal line spanning the axis.
Square	`mark_square()`	A scatter plot with filled squares.
Text	`mark_text()`	A scatter plot with points represented by text.
Tick	`mark_tick()`	A vertical or horizontal tick mark.
Trail	`mark_trail()`	A line with variable widths.

In addition, Altair provides the following composite marks:

Mark Name	Method	Description	Example
Box Plot	`mark_boxplot()`	A box plot.	Boxplot with Min/Max Whiskers
Error Band	`mark_errorband()`	A continuous band around a line.	Line Chart with Confidence Interval Band
Error Bar	`mark_errorbar()`	An error bar around a point.	Error Bars with Confidence Interval

In Altair, marks can be most conveniently specified by the mark_* methods of the Chart object (e.g. mark_bar), which take optional keyword arguments to configure the look of the marks.

Mark Properties#

This section lists standard mark properties for primitive mark types. Additionally, some marks may have special mark properties (listed in their documentation page).

General Mark Properties#

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Property	Type	Description
aria	anyOf(`boolean`, `ExprRef`)	A boolean flag indicating if ARIA attributes should be included (SVG output only). If `false`, the “aria-hidden” attribute will be set on the output SVG element, removing the mark item from the ARIA accessibility tree.
description	anyOf(`string`, `ExprRef`)	A text description of the mark item for ARIA accessibility (SVG output only). If specified, this property determines the “aria-label” attribute.
style	anyOf(`string`, array(`string`))	A string or array of strings indicating the name of custom styles to apply to the mark. A style is a named collection of mark property defaults defined within the style configuration. If style is an array, later styles will override earlier styles. Any mark properties explicitly defined within the `encoding` will override a style default. Default value: The mark’s name. For example, a bar mark will have style `"bar"` by default. Note: Any specified style will augment the default style. For example, a bar mark with `"style": "foo"` will receive from `config.style.bar` and `config.style.foo` (the specified style `"foo"` has higher precedence).
tooltip	anyOf(`number`, `string`, `boolean`, `TooltipContent`, `ExprRef`, `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`
clip	anyOf(`boolean`, `ExprRef`)	Whether a mark be clipped to the enclosing group’s width and height.
invalid	anyOf(`MarkInvalidDataMode`, `null`)	Invalid data mode, which defines how the marks and corresponding scales should represent invalid values (`null` and `NaN` in continuous scales without defined output for invalid values). `"filter"` — Exclude all invalid values from the visualization’s marks and scales. For path marks (for line, area, trail), this option will create paths that connect valid points, as if the data rows with invalid values do not exist. `"break-paths-filter-domains"` — Break path marks (for line, area, trail) at invalid values. For non-path marks, this is equivalent to `"filter"`. All scale domains will exclude these filtered data points. `"break-paths-show-domains"` — Break paths (for line, area, trail) at invalid values. Hide invalid values for non-path marks. All scale domains will include these filtered data points (for both path and non-path marks). `"show"` or `null` — Show all data points in the marks and scale domains. Each scale will use the output for invalid values defined in `config.scale.invalid` or, if unspecified, by default invalid values will produce the same visual values as zero (if the scale includes zero) or the minimum value (if the scale does not include zero). `"break-paths-show-path-domains"` (default) — This is equivalent to `"break-paths-show-domains"` for path-based marks (line/area/trail) and `"filter"` for non-path marks. Note: If any channel’s scale has an output for invalid values defined in `config.scale.invalid`, all values for the scales will be considered “valid” since they can produce a reasonable output for the scales. Thus, fields for such channels will not be filtered and will not cause path breaks.
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.

Position and Offset Properties#

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Property	Type	Description
x	anyOf(`number`, `string`, `ExprRef`)	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`, `string`, `ExprRef`)	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.
width	anyOf(`number`, `ExprRef`, `RelativeBandSize`)	Width of the marks. One of: A number representing a fixed pixel width. A relative band size definition. For example, `{band: 0.5}` represents half of the band.
height	anyOf(`number`, `ExprRef`, `RelativeBandSize`)	Height of the marks. One of: A number representing a fixed pixel height. A relative band size definition. For example, `{band: 0.5}` represents half of the band
y	anyOf(`number`, `string`, `ExprRef`)	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`, `string`, `ExprRef`)	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.
xOffset	anyOf(`number`, `ExprRef`)	Offset for x-position.
x2Offset	anyOf(`number`, `ExprRef`)	Offset for x2-position.
yOffset	anyOf(`number`, `ExprRef`)	Offset for y-position.
y2Offset	anyOf(`number`, `ExprRef`)	Offset for y2-position.

Color Properties#

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Property	Type	Description
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.
color	anyOf(`Color`, `Gradient`, `ExprRef`)	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`.
fill	anyOf(`Color`, `Gradient`, `null`, `ExprRef`)	Default fill color. This property has higher precedence than `config.color`. Set to `null` to remove fill. Default value: (None)
stroke	anyOf(`Color`, `Gradient`, `null`, `ExprRef`)	Default stroke color. This property has higher precedence than `config.color`. Set to `null` to remove stroke. Default value: (None)
blend	anyOf(`Blend`, `ExprRef`)	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"`
opacity	anyOf(`number`, `ExprRef`)	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.
fillOpacity	anyOf(`number`, `ExprRef`)	The fill opacity (value between [0,1]). Default value: `1`
strokeOpacity	anyOf(`number`, `ExprRef`)	The stroke opacity (value between [0,1]). Default value: `1`

Stroke Style Properties#

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Property	Type	Description
strokeCap	anyOf(`StrokeCap`, `ExprRef`)	The stroke cap for line ending style. One of `"butt"`, `"round"`, or `"square"`. Default value: `"butt"`
strokeDash	anyOf(array(`number`), `ExprRef`)	An array of alternating stroke, space lengths for creating dashed or dotted lines.
strokeDashOffset	anyOf(`number`, `ExprRef`)	The offset (in pixels) into which to begin drawing with the stroke dash array.
strokeJoin	anyOf(`StrokeJoin`, `ExprRef`)	The stroke line join method. One of `"miter"`, `"round"` or `"bevel"`. Default value: `"miter"`
strokeMiterLimit	anyOf(`number`, `ExprRef`)	The miter limit at which to bevel a line join.
strokeWidth	anyOf(`number`, `ExprRef`)	The stroke width, in pixels.

Hyperlink Properties#

Marks can act as hyperlinks when the href property or channel is defined. When the href property is specified, the cursor mark property is set to "pointer" by default to serve as affordance for hyperlinks.

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Property	Type	Description
href	anyOf(`URI`, `ExprRef`)	A URL to load upon mouse click. If defined, the mark acts as a hyperlink.
cursor	anyOf(`Cursor`, `ExprRef`)	The mouse cursor used over the mark. Any valid CSS cursor type can be used.