The Symbol Library¶

Common parameters¶

Some common options and widgets are available to build a symbol layer, regardless it’s of marker, line or fill sub-type:

• the color selector widget to ease color manipulation
• Units: it can be Millimeter, Pixels or Map unit
• the ^{data-defined override} widget near almost all options, extending capabilities of customizing each symbol (see Data defined override setup for more information)

Marker Symbols¶

Appropriate for point geometry features, marker symbols have several Symbol layer types:

• Simple marker (default);
• Ellipse marker: a simple marker symbol layer, with customizable width and height;
• Filled marker: similar to the simple marker symbol layer, except that it uses a fill sub symbol to render the marker. This allows use of all the existing QGIS fill (and outline) styles for rendering markers, e.g. gradient or shapeburst fills;
• Font marker: use installed fonts as marker symbols;
• Geometry generator (see The Geometry Generator);
• Vector Field marker (see The Vector Field Marker);

• SVG marker: provides you with images from your SVG paths (set in Settings ‣ Options ‣ System menu) to render as marker symbol. Each SVG file colors and outline can be adapted.

  Note

  Requirements for a customizable SVG marker symbol

  To have the possibility to change the colors of a SVG marker, you have to add the placeholders param(fill) for fill color, param(outline) for outline color and param(outline-width) for stroke width. These placeholders can optionally be followed by a default value, e.g.:

  <svg width="100%" height="100%">
  <rect fill="param(fill) #ff0000" stroke="param(outline) #00ff00" stroke-width="param(stroke-width) 10" width="100" height="100">
  </rect>
  </svg>
  

For each marker symbol layer type, you can set some of the following properties:

• Color for the fill and/or stroke, using all the capabilities of the Color Selector widget;
• Size
• Outline style
• Outline width
• Join style
• Rotation
• Offset X,Y: You can shift the symbol in the x- or y- direction;
• Anchor point.

In most of the marker symbols dialog, you also have a frame with previews of predefined symbols you can choose from.

Line Symbols¶

Appropriate for line geometry features, line symbols have following symbol layer types:

• Simple line (default): available settings are:
  • Color
  • Pen width
  • Pen style
  • Join style
  • Cap style
  • Offset
  • Use custom dash pattern: overrides the Pen style setting with a custom dash.

• Arrow: draws lines as curved (or not) arrows with a single or a double head with configurable width, length and thickness. To create a curved arrow the line feature must have at least three vertices. It also uses a fill symbol such as gradients or shapeburst to render the arrow body. Combined with the geometry generator, this type of layer symbol helps you representing flow maps;
• Geometry generator (see The Geometry Generator);
• Marker line: displays a marker symbol along the line. It can be at a regular distance or based on its geometry: first, last or each vertex, on central point or on every curve point. You can set an offset along the line for the marker symbol, or offset the line itself. The Rotate marker option allows you to set whether the marker symbol should follow the line orientation or not.

Fill Symbols¶

Appropriate for polygon geometry features, fill symbols have also several symbol layer types:

• Simple fill (default): the following settings are available:

  • Fill color
  • Outline color
  • Fill style
  • Outline style
  • Outline width
  • Join style
  • Offset X,Y

• Centroid fill: places a marker symbol at the centroid of the visible feature. The position of the marker may however not be the real centroid of the feature because calculation takes into account the polygon(s) clipped to area visible in map canvas for rendering and ignores holes. Use The Geometry Generator if you want the exact centroid.

  The marker can be placed on every part of a multi-part feature or only on its biggest part, and forced to be inside the polygon;

• Geometry generator (see geometry_generator_symbol);

• Gradient fill: uses a radial, linear or conical gradient, based on either simple two color gradients or a predefined gradient color ramp to fill polygon layers. Gradient can be rotated and applied on a single feature basis or across the whole map extent. Also start and end points can be set via coordinates or using the centroid (of feature or map);

• Line pattern fill: fills the polygon with a hatching pattern of line symbol layer. You can set the spacing between lines and an offset from the feature boundary;

• Point pattern fill: fills the polygon with a hatching pattern of marker symbol layer. You can set the spacing between lines and an offset from the feature boundary;

• Raster image fill: you can fill polygons with a tiled raster image. Options include (data defined) file name, opacity, image size (in pixels, mm or map units), coordinate mode (feature or view) and rotation;

• SVG fill: fills the polygon using SVG markers;

• Shapeburst fill: this option buffered a gradient fill, where a gradient is drawn from the boundary of a polygon towards the polygon’s centre. Configurable parameters include distance from the boundary to shade, use of color ramps or simple two color gradients, optional blurring of the fill and offsets;

• Outline: Arrow: uses a line arrow symbol layer to represent the polygon boundary;

• Outline: Marker line: uses a marker line symbol layer to represent the polygon boundary;

• Outline: simple line: uses a simple line symbol layer to represent the polygon boundary. The Draw line only inside polygon option helps polygon borders inside the polygon and can be useful to clearly represent adjacent polygon boundaries.

The Geometry Generator¶

Available with all types of symbols, the geometry generator symbol layer allows to use expression syntax to generate a geometry on the fly during the rendering process. The resulting geometry does not have to match with the original geometry type and you can add several differently modified symbol layers on top of each other.

Some examples:

-- render the centroid of a feature
centroid( $geometry )

-- visually overlap features within a 100 map units distance from a point
-- feature, i.e generate a 100m buffer around the point
buffer( $geometry, 100 )

-- Given polygon layer1( id1, layer2_id, ...) and layer2( id2, fieldn...)
-- render layer1 with a line joining centroids of both where layer2_id = id2
make_line( centroid( $geometry ),
           centroid( geometry( get_feature( 'layer2', 'id2', attribute(
               $currentfeature, 'layer2_id') ) )
         )

The Vector Field Marker¶

The vector field marker is used to display vector field data such as earth deformation, tidal flows, and the like. It displays the vectors as lines (preferably arrows) that are scaled and oriented according to selected attributes of data points. It can only be used to render point data; line and polygon layers are not drawn by this symbology.

The vector field is defined by attributes in the data, which can represent the field either by:

• cartesian components (x and y components of the field)
• or polar coordinates: in this case, attributes define Length and Angle. The angle may be measured either clockwise from north, or Counterclockwise from east, and may be either in degrees or radians.
• or as height only data, which displays a vertical arrow scaled using an attribute of the data. This is appropriate for displaying the vertical component of deformation, for example.

The magnitude of field can be scaled up or down to an appropriate size for viewing the field.