Image Mark

Image marks allow external images, such as icons or photographs, to be included in Vega visualizations. Image files such as PNG or JPG images can be loaded from provided URLs, or specified directly as data properties.


Type-Specific Mark Properties

Property Type Description
url URL The URL of the image file.
image Canvas | Image The image instance to show. This property can be used to include dynamically generated images. This property is ignored if url is specified. ≥ 5.8
aspect Boolean A boolean flag (default true) indicating if the image aspect ratio should be preserved across sizes. If true and only one of the dimensional (width or height) properties are defined, the other dimensional property will be calculated to match the aspect ratio of the loaded image file.
smooth Boolean A boolean flag (default true) indicating if the image should be smoothed when resized. If false, individual pixels should be scaled directly rather than interpolated with smoothing. For SVG rendering, this option may not work in some browsers due to lack of standardization. ≥ 5.8
align String The horizontal alignment of the image. One of left, center, or right. The default value is left.
baseline String The vertical alignment of the image. One of top, middle, or bottom. The default value is top.

General Mark Properties

Property Type Description
x Number The primary x-coordinate in pixels.
x2 Number The secondary x-coordinate in pixels.
xc Number The center x-coordinate. Incompatible with x and x2.
width Number The width of the mark in pixels, if supported.
y Number The primary y-coordinate in pixels.
y2 Number The secondary y-coordinate in pixels.
yc Number The center y-coordinate. Incompatible with y and y2.
height Number The height of the mark in pixels, if supported.
opacity Number The mark opacity from 0 (transparent) to 1 (opaque).
fill Color The fill color.
fillOpacity Number The fill opacity from 0 (transparent) to 1 (opaque).
stroke Color The stroke color.
strokeOpacity Number The stroke opacity from 0 (transparent) to 1 (opaque).
strokeWidth Number The stroke width in pixels.
strokeCap String The stroke cap for line ending style. One of butt (default), round or square.
strokeDash Number[ ] An array of [stroke, space] lengths for creating dashed or dotted lines.
strokeDashOffset Number The pixel offset at which to start the stroke dash array.
strokeJoin String The stroke line join method. One of miter (default), round or bevel.
strokeMiterLimit Number The miter limit at which to bevel a line join.
blend String The color blend mode for drawing an item on its current background. Any valid CSS mix-blend-mode value except for "normal" can be used. The default value null maps to blend values of normal for SVG and source-over for Canvas.
cursor String The mouse cursor used over the mark. Any valid CSS cursor type can be used.
href URL A URL to load upon mouse click. If defined, the mark acts as a hyperlink.
tooltip Any The tooltip text to show upon mouse hover. If the value is an object (other than a Date or an array), then all key-value pairs in the object will be shown in the tooltip, one per line (e.g., "key1: value1\nkey2: value2"). Array values will be shown in brackets [value1, value2, ...]. Other values will be coerced to strings. Nested object values will not be recursively printed.
zindex Number An integer z-index indicating the layering order of sibling mark items. The default value is 0. Higher values (1) will cause marks to be drawn on top of those with lower z-index values. Setting the z-index as an encoding property only affects ordering among sibling mark items; it will not change the layering relative to other mark definitions. Unlike the mark-level sort property, zindex changes the rendering order only; it does not otherwise change mark item order (such as line or area point order). The most common use of zindex is to ensure that a mark is drawn over its siblings when selected, such as by mouse hover.

For marks that support width and height settings (including rect and area), the horizontal dimensions are determined (in order of precedence) by the x and x2 properties, the x and width properties, the x2 and width properties, or the xc and width properties. If all three of x, x2 and width are specified, the width value is ignored. The y, y2, yc and height properties are treated similarly.

For marks that do not support width or height (including path and arc) similar calculations are applied, but are only used to determine the mark’s ultimate x and y position. The width property may affect the final x position, but otherwise is not visualized.

When using multiple spatial properties along the same dimension (x and x2, or y and y2), the properties must be specified in the same encoding set; for example, all within "enter": {...} or all within "update": {...}. Dividing the properties across encoding sets can cause unexpected behavior.

Accessibility Properties ≥ 5.11

Accessibility properties are used to determine ARIA (Accessible Rich Internet Applications) attributes when using Vega to render SVG output. Vega will automatically generate ARIA attributes for container SVG <g> elements for each mark definition; this can be configured using mark-level accessibility properties. Use the properties below in encode sets to add ARIA attributes for individual mark items.

Property Type Description
aria Boolean A boolean flag (default true) 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 String A text description of the mark item for ARIA accessibility (SVG output only). If specified, this property determines the “aria-label” attribute.