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marks Property
Marks visually encode data using geometric primitives.
General JSON format:
"marks": [
{
"type": points | line | polys | symbol,
"from": { data: <dataSourceID> },
"properties": { <propName>: <propVal> }, ... { <propName>: <propVal> }
"transform": { <transformType>: <transformName> }
},
{
...
}
],
A Vega
marks
specification includes the following properties:Property | Data Type | Required | Description |
string | X | Graphical marks type or shape:
| |
object | | Database table associated with the marks. | |
object | X | Visual encoding rules. Valid properties depend on marks type . | |
object | | Transforms applied to a mark. |
Marks are rendered in marks property array order.
Marks property values can be constants or as data references. You can use the scales property to transform marks property values to the visualization area.
Apply the
x
and y
scales to the x
and y
database table columns to scale the data to the visualization area width and height. For example:const exampleVega = {
"width:" 384,
"height:" 564,
"data:" [ ... elided ... ],
"scales:" [
{
"name:" "x",
"type:" "linear",
"domain:" [-3650484.1235206556,7413325.514451755],
"range:" "width"
},
{
"name:" "y",
"type:" "linear",
"domain:" [-5778161.9183506705, 10471808.487466192],
"range:" "height"
}
],
"marks:" [
{
"type:" "points",
"from:" { "data:" "tweets" },
"properties:" {
"x:" { "scale:" "x", "field:" "x" },
"y:" { "scale:" "y","field:" "y"}
}
}
]
};
Marks must include a
type
property that specifies the geometric primitive to use to render the data.Specify
x
and y
coordinate values using either constants, or domain and range values of a data
reference. If the from
property is not specified, the x
and y
properties
fields must be constants.Define a point with size, color, and opacity:
{
"width" : 1024,
"height" : 1024,
"data": [
{
"name" : "table",
"values": [
{"x": 412, "y": 512, "val": 0.9,"color": "red"},
{"x": 512, "y": 512, "val": 0.3, "color": "violet"},
{"x": 612, "y": 512, "val": 0.5,"color": "green"}
]
}
],
"marks" : [
{
"type" : "points",
"from" : {"data" : "table"},
"properties" : {
"x" : { "field" : "x" },
"y" : { "field" : "y" },
"fillColor" : {
"field" : "color"
},
"size" : 150.0,
"fillOpacity" : {
"field" : "val"
},
"opacity" : 0.8
}
}
]
}
Associate the
points
geometric primitive with tweets
data items.vegaSpec = {
"width": 384,
"height": 564,
"data": [
{
"name": "tweets",
"sql": "SELECT ... elided ... "
}
],
"scales": [ ... elided ... ],
"marks": [
{
"type": "points",
"from": { data: "tweets" },
"properties": { ... elided ... }
},
{ ... elided ... }
]
};
Specifying the
data
format
property as lines
causes the rendering engine to assume a lines
database table layout and to extract line-related columns from the table.Specify
x
and y
coordinate values using either constants, or domain and range values of a data
reference. If the from
property is not specified, the x
and y
properties
fields must be constants.{
"type": "lines",
"from": {"data": "table"},
"properties": {
"x": {
"field": "x",
"scale": "x"
},
"y": {
"field": "y",
"scale": "y"
},
"strokeColor": {
"scale": "strokeColor",
"field": "color"
},
"strokeWidth": 2,
"lineJoin": "miter",
"miterLimit": 10
}
}
The
polys
type renders data as a polygon.
When the data
format property is polys
, the rendering engine assumes a polys
database table layout and extracts the poly-related columns from the table. A polys
database table layout implies that the first data column is the vertex x- and y-positions. The vertices are interleaved x and y values, such that vertex[0] = vert0.x
, vertex[1] = vert0.y
, vertex[2] = vert1.x
, and vertex[3] = vert1.y
, for example. The next three positions of a polys
database table are the triangulated indices, and line loop and drawing information for unpacking multiple, associated polygons that can be packed as a single data item.const exampleVega = {
"width": 1004,
"height": 336,
"data": [
{
"name": "polys",
"format": "polys",
"sql": "SELECT ... elided ..."
}
],
"scales": [ ... elided ... ]
"marks": [
{
"type": "polys",
"from": {
"data": "polys"
},
"properties": {
"x": {
"scale": "x",
"field": "x"
},
"y": {
"scale": "y",
"field": "y"
},
"fillColor": {
"scale": "polys_fillColor",
"field": "avgContrib"
},
"strokeColor": "white",
"strokeWidth": 0,
"lineJoin": "miter",
"miterLimit": 10
}
}
]
}
Currently, in
symbol
mark types, strokes are not visible beneath other marks, regardless of opacity settings.Specify
x
and y
coordinate values using either constants or domain and range values of a data
reference. If the from
property is not specified, the x
and y
properties
fields must be specified using constant values.const exampleVega = {
"width": 733,
"height": 530,
"data": [
{
"name": "heatmap_query",
"sql": "SELECT ... elided ... "
}
],
"scales": [ ... elided ... ],
],
"marks": [
{
"type": "symbol",
"from": {
"data": "heatmap_query"
},
"properties": {
"shape": "square",
"x": { "field": "x" },
"y": { "field": "y" },
"width": 1,
"height": 1,
"fillColor": { "scale": "heat_color", "field": "cnt" }
}
}
]
};
The following example defines symbol mark types including fill, stroke, and general opacity properties:
{
"width" : 1024,
"height" : 1024,
"data": [
{
"name" : "table",
"values": [
{"x": 200, "x2": 0.0, "y": 200.0, "y2": 0.0, "val" : 0, "color" : "red", "color2": "yellow", "opacity": 1.0, "fillOpacity":0.75, "strokeOpacity": 0.25},
{"x": 220.806, "x2": 0.0, "y": 263.75, "y2": 0.0, "val" : 1, "color" : "blue", "color2": "green", "opacity": 0.5, "fillOpacity": 0.5, "strokeOpacity": 0.5},
{"x": 240.61216, "x2": 0.0, "y": 327.5, "y2": 0.0, "val" : 0, "color" : "maroon", "color2": "magenta", "opacity": 0.1, "fillOpacity": 0.25, "strokeOpacity": 0.75}
]
}
],
"marks" : [
{
"type" : "symbol",
"from" : {"data" : "table"},
"properties" : {
"shape" : "circle",
"xc" : { "field" : "x" },
"yc" : { "field" : "y" },
"width": 150.0,
"height": 150.0,
"opacity": 0.9,
"fillOpacity": {
"field": "fillOpacity"
},
"fillColor" : {
"field": "color2"
},
"strokeWidth" : 10.0,
"strokeColor" : {
"field": "color"
},
"strokeOpacity": {
"field": "strokeOpacity"
}
}
}
]
}
The
from
field specifies the input database table to use.Data Source Field | Data Type | Description |
data | string |
Example
Use the
tweets
database table for marks input data.vegaSpec = {
"width": 384,
"height": 564,
"data": [
{
"name": "tweets",
"sql": "SELECT ... elided ... "
}
],
"scales": [ ... elided ... ],
"marks": [
{
"type": "polys",
"from": {"data": "tweets"},
"properties": { ... elided ... }
}
]
};
If
from
is not specified, the data source is implicitly a single point with the value defined in the points
properties.The
properties
property specifies type-dependent visual encoding that define the position and appearance of mark instances. The property value is specified using one of the Value Reference options.Typically, a single mark instance is generated per input data element, except for
polys
, which uses multiple data elements to represent a line or area shape.The following table describes the various marks
properties
and lists the types for which the property is valid.Property | Data Type | Valid Primitive Types | Description |
angle | number | symbol | Amount of rotation about the defined center of rotation. The center of rotation depends on the properties that specify the symbol location:
Must be a numerical constant or a scale that provides numerical values. In the following example, the triangle-down symbol is rotated 30 degrees about the downward point: |
angleUnit | string | symbol | Optional. Unit of measure for the rotation of a symbol around the center of rotation, defined in angle . Either degrees (default) or radians . |
fillColor | color | points, polys, symbol | Fill color. Must be a scale/data reference, a string, or a color represented by a 32-bit integer or unsigned integer. See Color Value Reference. |
fillOpacity | number | points, polys, symbol | The fill opacity, from transparent ( 0 ) to opaque (1 ). If used with opacity , the values are multiplied together to determine final opacity. |
height | number | symbol | Mark height, in pixels. |
lineJoin | string | line, polys, symbol | Line join method:
|
miterLimit | number | line, polys, symbol | The miter limit at which to bevel a line join, in pixels. Must be a positive number. Default = 10.0 |
opacity | number | all | The line opacity as a whole, from transparent ( 0 ) to opaque (1 ). If used with fillOpacity (points , polys , symbol ) or strokeOpacity (lines), the values are multiplied together to determine final opacity. |
shape | string | symbol | Shape name:
|
size | number | points | Graphical primitive size, in pixels. Must be a scale/data reference or a number. |
stroke | color | symbol | Stroke color. |
strokeColor | color | line, polys | Stroke color. Must be a scale/data reference, a string, or a color represented by a 32-bit integer or unsigned integer. See Color Value Reference. Default color = white |
strokeOpacity | number | line, polys, symbol | Stroke opacity, from transparent ( 0 ) to opaque (1 ). If used with opacity , the values are multiplied together to determine final opacity. |
strokeWidth | number | line, polys, symbol | Stroke width, in pixels. Must be a scale/data reference or a number. |
width | number | symbol | Mark width, in pixels. |
x | number | all | Primary x-coordinate, in pixels. Must be a scale/data reference for polys , or a scale/data reference or a number for points , lines , or symbol . See Value Reference. |
x2 | number | symbol | |
xc | number | symbol | |
y | number | all | Primary y-coordinate, in pixels. Must be a scale/data reference for polys , or a scale/data reference or a number for points , lines , or symbol . See Value Reference. |
y2 | number | symbol | |
yc | number | symbol | |
z | number | points, symbol | Primary depth-coordinate, in pixels. Must be a scale/data reference or a number. See Value Reference. |
A value reference describes how to specify marks
properties
values. The value can be a constant or data object reference:Name | Type Description | |
value | Any | Constant value. If field is specified, value is ignored. |
field | Perform a lookup on the current data value. The marks from property determines the source data table and the field name must be a column defined in the data property. | |
scale | Name of a scale transform to apply to the mark. If the input is an object, it indicates a field value from which to dynamically look up the scale name and follows the Field Reference format. |
Examples:
Statically set the point
fillColor
and size
."marks:" [
{
"type:" "points",
"from:" {
"data:" "tweets"
},
"properties:" {
... elided ...
"fillColor": "blue",
"size": 3
}
}
}
]
For the
x
marks property, apply the x
scale transform to the implicit x-coordinate data column."marks": [
{
"type": "polys",
"from": {
"data": "polys"
},
"properties": {
"x": {
"scale": "x",
"field": "x"
},
... elided ...
}
}
]
A field reference is either a string literal or an object. For object values, the following properties are supported:
Property | Type | Description |
Property Name | FieldRef | Perform a lookup on the property name. This is the default operation when a field reference is a string. |
Typically, color values are specified as a single RGB color value. To specify specific color fields or use a different color space, use one of the following color value reference formats:
Property Value Field | Data Type | Description |
field | string | Name of the attribute from the data: sql field. |
colorSpace | string | Space in which the color is defined:
|
Examples
Set the red and blue channels of an RGB color as constants, and uses a scale transform to determine the green channel:
"fill": {
"r": {"value": 255},
"g": {"scale": "green", "field": "g"},
"b": {"value": 0}
}
Use the
rgb
color space for the color
field:"fillColor": {
"field": "color",
"colorSpace": "rgb"
}
The
transform
object specifies any Vega projections to be applied to the mark. Each transform is specified as a key:value pair in the transform
object:},
"transform": {
"<key>": "<value>"
}
The value references an existing Vega object by name.
For example, the following transform references the projection
my_mercator_projection
defined in the top-level Vega projections
property."projections": [
{
"name": "my_mercator_projection",
"type": "mercator",
"bounds": {
"x": [-120.0, 120.0],
"y": [-20.0, 20.0]
}
}
]
"marks": [
{
"type": "symbol",
"from": { "data": "fec_contributions_oct" },
"properties": { ... elided ... }
"transform": {
"projection": "my_mercator_projection"
}
}
]
Currently, the only supported transform is
projection
.Last modified 2yr ago