Mark

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Marks are the basic visual building block of a visualization. They provide basic shapes whose properties (such as position, size, and color) can be used to visually encode data, either from a data field, or a constant value.

The supported mark types are "area", "bar", "circle", "line", "point", "rect", "rule", "square", "text", "tick", and "geoshape". In general, one mark instance is generated per input data element. However, line and area marks represent multiple data elements as a contiguous line or shape.

// Single View Specification
{
  "data": ... ,
  "mark": ... ,       // mark
  "encoding": ... ,
  ...
}

The mark property of a single view specification can either be (1) a string describing a mark type or (2) a mark definition object.

For example, a bar chart has mark as a simple string "bar".

Documentation Overview

Mark Definition Object

// Single View Specification
{
  ...
  "mark": {
    "type": ...,       // mark
    ...
  },
  ...
}

To customize properties of a mark, users can set mark to be a mark definition object instead of a string describing mark type. The rest of this section lists all standard mark properties. In addition, some marks may have special mark properties (listed in their documentation page).

Note: If mark property encoding channels are specified, these mark properties will be overridden.

General Mark Properties

Property Type Description
type String

Required. The mark type. One of "bar", "circle", "square", "tick", "line", "area", "point", "geoshape", "rule", and "text".

style String | 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).

clip Boolean

Whether a mark be clipped to the enclosing group’s width and height.

Color Properties

Property Type Description
filled Boolean

Whether the mark’s color should be used as fill color instead of stroke color.

Default value: true for all marks except point and false for point.

Applicable for: bar, point, circle, square, and area marks.

Note: This property cannot be used in a style config.

color String

Default color. Note that fill and stroke have higher precedence than color and will override color.

Default value: "#4682b4"

Note: This property cannot be used in a style config.

fill String

Default Fill Color. This has higher precedence than config.color

Default value: (None)

stroke String

Default Stroke Color. This has higher precedence than config.color

Default value: (None)

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.

fillOpacity Number

The fill opacity (value between [0,1]).

Default value: 1

strokeOpacity Number

The stroke opacity (value between [0,1]).

Default value: 1

Stroke Style Properties

Property Type Description
strokeWidth Number

The stroke width, in pixels.

strokeDash 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.

Marks can act as hyperlinks when the href property or channel is defined. A cursor property can also be provided to serve as affordance for the links.

Property Type Description
href String

A URL to load upon mouse click. If defined, the mark acts as a hyperlink.

cursor String

The mouse cursor used over the mark. Any valid CSS cursor type can be used.

Mark Config

// Top-level View Specification
{
  ...
  "config": {
    "mark": ...,
    "area": ...,
    "bar": ...,
    "circle": ...,
    "line": ...,
    "point": ...,
    "rect": ...,
    "rule": ...,
    "geoshape": ...,
    "square": ...,
    "text": ...,
    "tick": ...
  }
}

The mark property of the config object sets the default properties for all marks. In addition, the config object also provides mark-specific config using its mark type as the property name (e.g., config.area) for defining default properties for each mark.

The global mark config (config.mark) supports all standard mark properties (except type, style, clip, and orient). For mark-specific config, please see the documentation for each mark type.

Note: If mark properties in mark definition or mark property encoding channels are specified, these config values will be overridden.

Mark Style Config

{
  // Top Level Specification
  "config": {
    "style": {
      ...
    }
    ...
  }
}

In addition to the default mark properties above, default values can be further customized using named styles defined under the style property in the config object.

Property Type Description
style Object

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.

For example, to set a default shape and stroke width for point marks with a style named "triangle":

{
  "style": {
    "triangle": {
      "shape": "triangle-up",
      "strokeWidth": 2
    }
  }
}

Styles can then be invoked by including a style property within a mark definition object.

In addition to custom style names, Vega-Lite includes the following built-in style names:

  • "guide-label": style for axis, legend, and header labels
  • "guide-title": style for axis, legend, and header titles

Example: Styling Labels

You can use text marks as labels for other marks by setting style for the marks and using style config to configure offset (dx or dy), align, and baseline.

See also: a similar example that uses mark definition to configure offset, align, and baseline.