Symbolizers

The basic unit of visualization is the symbolizer. There are five types of symbolizers: Point, Line, Polygon, Raster, and Text.

Symbolizers are contained inside rules. A rule can contain one or many symbolizers.

Note

The most common use case for multiple symbolizers is a geometry (point/line/polygon) symbolizer to draw the features plus a text symbolizer for labeling these features.

Use of multiple symbolizers

Drawing order

The order of symbolizers significant, and also the order of your data.

For each feature the rules are evaluated resulting in a list of symbolizers that will be used to draw that feature. The symbolizers are drawn in the order provided.

Consider the following two symbolizers:

symbolizers:
- point:
    symbols:
    - mark:
        shape: square
        fill-color: '#FFCC00'
- point:
    symbols:
    - mark:
        shape: triangle
        fill-color: '#FF3300'

When drawing three points these symbolizers will be applied in order on each feature:

1. Feature 1 is drawn as a square, followed by a triangle:

   Feature 1 buffer rendering

2. Feature 2 is drawn as a square, followed by a triangle. Notice the slight overlap with Feature 1:

   Feature 2 buffer rendering

3. Feature 3 is drawn as a square, followed by a triangle:

   Feature 3 buffer rendering

Note

In the final image, Feature 1 and Feature 2 have a slight overlap. This overlap is determined by data order which we have no control over. If you need to control the overlap review the Feature Styles section on managing "z-order".

Feature style controlling z-order

Matching symbolizers and geometries

It is common to match the symbolizer with the type of geometries contained in the layer, but this is not required. The following table illustrates what will happen when a geometry symbolizer is matched up with another type of geometry.

	Points	Lines	Polygon	Raster
Point Symbolizer	Points	Midpoint of the lines	Centroid of the polygons	Centroid of the raster
Line Symbolizer	n/a	Lines	Outline (stroke) of the polygons	Outline (stroke) of the raster
Polygon Symbolizer	n/a	Will "close" the line and style as a polygon	Polygons	Will "outline" the raster and style as a polygon
Raster Symbolizer	n/a	n/a	n/a	Transform raster values to color channels for display
Text Symbolizer	Label at point location	Label at midpoint of lines	Label at centroid of polygons	Label at centroid of raster outline

Syntax

The following is the basic syntax common to all symbolizers. Note that the contents of the block are not all expanded here and that each kind of symbolizer provides additional syntax.

geometry: <cql>
uom: <text>
..
x-composite: <text>
x-composite-base: <boolean>
x-inclusion: <text>

Where:

Property	Required?	Description	Default value
geometry	No	Specifies which attribute to use as the geometry (see Geometry transformations in SLD)	First geometry attribute found (usually named geom or the_geom)
uom	No	Unit of measure used for width calculations (see Specifying symbolizer sizes in ground units)	pixel

Additional "vendor options" properties for Color compositing and color blending:

Property	Required?	Description	Default value
x-composite	No	Allows for both alpha compositing and color blending options between symbolizers.	N/A
x-composite-base	No	Allows the rendering engine to use the symbolizer mapping to define a "base" buffer for subsequent compositing and blending using x-composite. See the section on Feature Styles for more details.	false

Additional "vendor options" properties for Rendering Selection:

Property	Required?	Description	Default value
x-inclusion	No	Define if rule should be included in style for legendOnly or mapOnly.	normal