PointSymbolizer

A PointSymbolizer styles features as points. Points are depicted as graphic symbols at a single location on the map.

Syntax

A <PointSymbolizer> contains an optional <Geometry> element, and a required <Graphic> element specifying the point symbology.

Tag

Required?

Description

<Geometry>

No

Specifies the geometry to be rendered.

<Graphic>

Yes

Specifies the styling for the point symbol.

Geometry

The <Geometry> element is optional. If present, it specifies the featuretype property from which to obtain the geometry to style using a <PropertyName> element. See also Geometry transformations in SLD for GeoServer extensions for specifying geometry.

Any kind of geometry may be styled with a <PointSymbolizer>. For non-point geometries, a representative point is used (such as the centroid of a line or polygon).

Graphic

Symbology is specified using a <Graphic> element. The symbol is specified by either an <ExternalGraphic> or a <Mark> element. External Graphics are image files (in a format such as PNG or SVG) that contain the shape and color information defining how to render a symbol. Marks are vector shapes whose stroke and fill are defined explicitly in the symbolizer.

There are five possible sub-elements of the <Graphic> element. One of <ExternalGraphic> or <Mark> must be specified; the others are optional.

Tag

Required?

Description

<ExternalGraphic>

No (when using <Mark>)

Specifies an external image file to use as the symbol.

<Mark>

No (when using <ExternalGraphic>)

Specifies a named shape to use as the symbol.

<Opacity>

No

Specifies the opacity (transparency) of the symbol. Values range from 0 (completely transparent) to 1 (completely opaque). Value may contain expressions. Default is 1 (opaque).

<Size>

No

Specifies the size of the symbol, in pixels. When used with an image file, this specifies the height of the image, with the width being scaled accordingly. if omitted the native symbol size is used. Value may contain expressions.

<Rotation>

No

Specifies the rotation of the symbol about its center point, in decimal degrees. Positive values indicate rotation in the clockwise direction, negative values indicate counter-clockwise rotation. Value may contain expressions. Default is 0.

ExternalGraphic

External Graphics are image files (in formats such as PNG or SVG) that contain the shape and color information defining how to render a symbol. For GeoServer extensions for specifying external graphics, see Graphic symbology in GeoServer.

The <ExternalGraphic> element has the sub-elements:

Tag

Required?

Description

<OnlineResource>

Yes

The xlink:href attribute specifies the location of the image file. The value can be either a URL or a local pathname relative to the SLD directory. The value can contain CQL expressions delimited by ${ }. The attribute xlink:type="simple" is also required. The element does not contain any content.

<Format>

Yes

The MIME type of the image format. Most standard web image formats are supported. Common MIME types are image/png, image/jpeg, image/gif, and image/svg+xml

Mark

Marks are predefined vector shapes identified by a well-known name. Their fill and stroke can be defined explicitly in the SLD. For GeoServer extensions for specifying mark symbols, see Graphic symbology in GeoServer.

The <Mark> element has the sub-elements:

Tag

Required?

Description

<WellKnownName>

No

The name of the shape. Standard SLD shapes are circle, square, triangle, star, cross, or x. Default is square.

<Fill>

No

Specifies how the symbol should be filled (for closed shapes). Options are to use <CssParameter name="fill"> to specify a solid fill color, or using <GraphicFill> for a tiled graphic fill. See the PolygonSymbolizer Fill for the full syntax.

<Stroke>

No

Specifies how the symbol linework should be drawn. Some options are using <CssParameter name="stroke"> to specify a stroke color, or using <GraphicStroke> for a repeated graphic. See the LineSymbolizer Stroke for the full syntax.

Example

The following symbolizer is taken from the Points section in the SLD Cookbook.

 1  <PointSymbolizer>
 2    <Graphic>
 3      <Mark>
 4        <WellKnownName>circle</WellKnownName>
 5        <Fill>
 6          <CssParameter name="fill">#FF0000</CssParameter>
 7        </Fill>
 8      </Mark>
 9      <Size>6</Size>
10    </Graphic>
11  </PointSymbolizer>

The symbolizer contains the required <Graphic> element. Inside this element is the <Mark> element and <Size> element, which are the minimum required element inside <Graphic> (when not using the <ExternalGraphic> element). The <Mark> element contains the <WellKnownName> element and a <Fill> element. No other element are required. In summary, this example specifies the following:

  1. Features will be rendered as points

  2. Points will be rendered as circles

  3. Circles will be rendered with a diameter of 6 pixels and filled with the color red

The next example uses an external graphic loaded from the file system:

1  <PointSymbolizer>
2    <Graphic>
3      <ExternalGraphic>
4        <OnlineResource xlink:type="simple"
5                        xlink:href="file:///var/www/htdocs/sun.png" />
6        <Format>image.png</Format>
7      </ExternalGraphic>
8    </Graphic>
9  </PointSymbolizer>

For file:// URLs, the file must be readable by the user the GeoServer process is running as. You can also use href:// URLs to reference remote graphics.

Further examples can be found in the Points section of the SLD Cookbook.

Using expressions in parameter values

Many SLD parameters allow their values to be of mixed type. This means that the element content can be:

  • a constant value expressed as a string

  • a filter expression

  • any combination of strings and filter expressions.

Using expressions in parameter values provides the ability to determine styling dynamically on a per-feature basis, by computing parameter values from feature properties. Using computed parameters is an alternative to using rules in some situations, and may provide a more compact SLD document.

GeoServer also supports using substitution variables provided in WMS requests. This is described in Variable substitution in SLD.

Previous: Filters
Next: LineSymbolizer