Styling a polygon layer

The Countries layer is a polygon layer, and therefore we use a polygon symbolizer to display it.

Viewing the existing style

  1. In the layers tab of Composer, click the style option for the countries layer to go to the style edit page. A simple default style is already associated with this layer.

    ../../../_images/poly_default1.png

    Default polygon style

    Note

    Your default color may vary.

  2. The default style will look something like this:

    name: Default Styler
    title: A yellow polygon style
    feature-styles:
    - name: name
      rules:
      - title: yellow polygon
        symbolizers:
        - polygon:
            stroke-color: '#000000'
            stroke-width: 0.5
            fill-color: '#FFFF00'
    

Name and Title

The feature style and individual elements within the style can be given name and title parameters. name is a machine reference to the style element and is not intended to be displayed. It should be lower case and contain no spaces. title is a human-readable description of a style element, and will be displayed by client applications.

  1. Modify the name and title elements in the default style:

    name: countries
    title: Countries style
    abstract: countries of the world
    feature-styles:
    - name: name
      rules:
      - title: Countries
        symbolizers:
        - polygon:
            stroke-color: '#000000'
            stroke-width: 0.5
            fill-color: '#FFFF00'
    

Setting basic styling

Polygon symbolizers provide options for styling both fill (inside) and stroke (outline) of features.

  1. Stroke styling is defined primarily by stroke-width, stroke-color, and stroke-opacity. Change the style to use a 0.5 pixel gray stroke:

    Note

    With no opacity set, the default will be 100% opaque.

      rules:
      - title: Countries
        symbolizers:
          polygon:
            stroke-color: '#777777'
            stroke-width: 0.5
    
  2. Fill styling is defined primarily by fill-color and fill-opacity. Change the style to use a 50% transparent brown fill:

      rules:
      - title: Countries
        symbolizers:
          polygon:
            stroke-color: '#777777'
            stroke-width: 0.5
            fill-color: '#EFEFC3'
            fill-opacity: 0.5
    
  3. Additional styling options are available for both stroke and fill, and can be found in the symbolizer reference. Use stroke-dasharray to change the line style to a dashed line of 4 pixels with 4 pixel gaps.

      rules:
      - title: Countries
        symbolizers:
          polygon:
            stroke-color: '#777777'
            stroke-width: 0.5
            fill-color: '#EFEFC3'
            fill-opacity: 0.5
            stroke-dasharray: '4 4'
    
  4. The complete style after these changes will be:

    name: countries
    title: Countries style
    abstract: countries of the world
    feature-styles:
    - name: name
      rules:
      - symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-width: 0.5
            stroke-dasharray: '4 4'
            fill-color: '#EFEFC3'
            fill-opacity: 0.5
    
  5. And the layer now will look like this:

    ../../../_images/poly_basic1.png

    Basic styled polygons

Adding labels

Labels can be applied to any layer using a text symbolizer. Typically you will want to use some data attribute as the label text, usually a name.

  1. Add a text symbolizer with a basic label using the NAME attribute:

    name: countries
    title: Countries style
    abstract: countries of the world
    feature-styles:
    - name: name
      rules:
      - symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-width: 0.5
            stroke-dasharray: '4 4'
            fill-color: '#EFEFC3'
            fill-opacity: 0.5
        - text:
            label: ${NAME}
    
  2. After this change, the map will look like this:

    ../../../_images/poly_label_basic1.png

    Basic labels

Styling labels

The default labeling parameters are not ideal, but a number of styling options are available.

  1. Add the following attributes to the text symbolizer:

    Parameter Description
    label: ${strToUpperCase(NAME)} Change the label text to uppercase
    font-size: 14 Change the font size to 14
    font-family: SansSerif Change the font to SansSerif
    font-weight: bold Make the font bold
    fill-color: '#333333' Change the font color to dark gray
  2. The above gives a much nicer font style, but the label placement is still poor. Add some additional options to fix this:

    Parameter Description
    x-autoWrap: 100 Wrap any labels wider than 100 pixels
    x-maxDisplacement: 200 Allow labels to shift up to 200 pixels to maintain best placement
    x-goodnessOfFit: 0.8 Only show labels with 0.8 or better fit
    x-labelPriority: ${10-LABELRANK} Select labels based on priority (uses the LABELRANK attribute of the data to determine this).
  3. With the label styling, the style now looks like this:

    name: countries
    title: Countries style
    abstract: countries of the world
    feature-styles:
    - name: name
      rules:
      - symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-width: 0.5
            stroke-dasharray: '4 4'
            fill-color: '#EFEFC3'
            fill-opacity: 0.5
        - text:
            label: ${strToUpperCase(NAME)}
            font-size: 14
            font-family: SansSerif
            font-weight: bold
            fill-color: '#333333'
            x-autoWrap: 100
            x-maxDisplacement: 200
            x-goodnessOfFit: 0.8
            x-labelPriority: ${10-LABELRANK}
    

And the labels now appear much clearer:

../../../_images/poly_label_styled1.png

Styled labels

Adding filters

Suppose we wish to display different colors for each country. The countries layer contains an attribute called MAPCOLOR7, which assigns each country a number from 1 to 7, such that no adjacent countries have the same number. We can use this attribute to control what color a country is using filters. Filters apply a condition to a rule, so that the symbolizers in that rule are only drawn if the filter evaluates to true.

  1. First, let’s split out the text symbolizer into its own rule. This won’t affect the visualization at all, but will make it easier to add the polygon filter rules in the next step.

    name: countries
    title: Countries style
    abstract: countries of the world
    feature-styles:
    - name: name
      rules:
      - symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-width: 0.5
            stroke-dasharray: '4 4'
            fill-color: '#EFEFC3'
            fill-opacity: 0.5
      - symbolizers:
        - text:
            label: ${strToUpperCase(NAME)}
            font-size: 14
            font-family: SansSerif
            font-weight: bold
            fill-color: '#333333'
            x-autoWrap: 100
            x-maxDisplacement: 200
            x-goodnessOfFit: 0.8
            x-labelPriority: ${10-LABELRANK}
    
  2. Replace the rule containing the polygon symbolizer with seven rules, corresponding to the seven possibilities of values for MAPCOLOR7. For each value, set the fill-color to the following:

    Filter Parameter
    MAPCOLOR7 = 1 fill-color: '#FFC3C3'
    MAPCOLOR7 = 2 fill-color: '#FFE3C3'
    MAPCOLOR7 = 3 fill-color: '#FFFFC3'
    MAPCOLOR7 = 4 fill-color: '#C3FFE3'
    MAPCOLOR7 = 5 fill-color: '#C3FFFF'
    MAPCOLOR7 = 6 fill-color: '#C3C3FF'
    MAPCOLOR7 = 7 fill-color: '#FFC3FF'
  3. After adding the filters, the style will look like:

    name: countries
    title: Countries style
    abstract: countries of the world
    feature-styles:
    - name: name
      rules:
      - filter: ${MAPCOLOR7 = 1}
        symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-dasharray: '4 4'
            stroke-width: 0.5
            fill-opacity: 0.5
            fill-color: '#FFC3C3'
      - filter: ${MAPCOLOR7 = 2}
        symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-dasharray: '4 4'
            stroke-width: 0.5
            fill-opacity: 0.5
            fill-color: '#FFE3C3'
      - filter: ${MAPCOLOR7 = 3}
        symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-dasharray: '4 4'
            stroke-width: 0.5
            fill-opacity: 0.5
            fill-color: '#FFFFC3'
      - filter: ${MAPCOLOR7 = 4}
        symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-dasharray: '4 4'
            stroke-width: 0.5
            fill-opacity: 0.5
            fill-color: '#C3FFE3'
      - filter: ${MAPCOLOR7 = 5}
        symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-dasharray: '4 4'
            stroke-width: 0.5
            fill-opacity: 0.5
            fill-color: '#C3FFFF'
      - filter: ${MAPCOLOR7 = 6}
        symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-dasharray: '4 4'
            stroke-width: 0.5
            fill-opacity: 0.5
            fill-color: '#C3C3FF'
      - filter: ${MAPCOLOR7 = 7}
        symbolizers:
        - polygon:
            stroke-color: '#777777'
            stroke-dasharray: '4 4'
            stroke-width: 0.5
            fill-opacity: 0.5
            fill-color: '#FFC3FF'
      - symbolizers:
        - text:
            label: ${strToUpperCase(NAME)}
            font-size: 14
            font-family: SansSerif
            font-weight: bold
            fill-color: '#333333'
            x-autoWrap: 100
            x-maxDisplacement: 200
            x-goodnessOfFit: 0.8
            x-labelPriority: ${10-LABELRANK}
    
    ../../../_images/poly_label_color1.png

    Adjacent countries will not have the same color

Reducing redundant content using variables

Much of the styling content in each of the filters used above is repeated. This repeated content can be reduced using variables.

  1. Add a directive block named polystyle to the beginning (top) of the style, above everything else:

    define: &polystyle
       stroke-color: '#777777'
       stroke-dasharray: '4 4'
       stroke-width: 0.5
       fill-opacity: 0.5
    
  2. For each of the seven filter rules, remove every property except fill-color and add <<: *polystyle. This will copy all the properties defined in our variable block to each of the rules. The style will now look like:

    define: &polystyle
      stroke-color: '#777777'
      stroke-dasharray: '4 4'
      stroke-width: 0.5
      fill-opacity: 0.5
    name: countries
    title: Countries style
    abstract: countries of the world
    feature-styles:
    - name: name
      rules:
      - filter: ${MAPCOLOR7 = 1}
        symbolizers:
        - polygon:
            <<: *polystyle
            fill-color: '#FFC3C3'
      - filter: ${MAPCOLOR7 = 2}
        symbolizers:
        - polygon:
            <<: *polystyle
            fill-color: '#FFE3C3'
      - filter: ${MAPCOLOR7 = 3}
        symbolizers:
        - polygon:
            <<: *polystyle
            fill-color: '#FFFFC3'
      - filter: ${MAPCOLOR7 = 4}
        symbolizers:
        - polygon:
            <<: *polystyle
            fill-color: '#C3FFE3'
      - filter: ${MAPCOLOR7 = 5}
        symbolizers:
        - polygon:
            <<: *polystyle
            fill-color: '#C3FFFF'
      - filter: ${MAPCOLOR7 = 6}
        symbolizers:
        - polygon:
            <<: *polystyle
            fill-color: '#C3C3FF'
      - filter: ${MAPCOLOR7 = 7}
        symbolizers:
        - polygon:
            <<: *polystyle
            fill-color: '#FFC3FF'
      - symbolizers:
        - text:
            label: ${strToUpperCase(NAME)}
            font-size: 14
            font-family: SansSerif
            font-weight: bold
            fill-color: '#333333'
            x-autoWrap: 100
    

Compacting thematic styles with transformation functions

While filters are very useful, the required syntax is still quite long, and much of the content is redundant. The exact same functionality can be accomplished much more concisely using the recode function.

  1. Remove all of the polygon rules and the variable at the top, and replace with our original rule:

    name: countries
    title: Countries style
    abstract: countries of the world
    feature-styles:
    - name: name
      rules:
      - symbolizers:
         - polygon:
            stroke-color: '#777777'
            stroke-dasharray: '4 4'
            stroke-width: 0.5
            fill-color: '#EFEFC3'
            fill-opacity: 0.5
      - symbolizers:
        - text:
            label: ${strToUpperCase(NAME)}
            font-size: 14
            font-family: SansSerif
            font-weight: bold
            fill-color: '#333333'
            x-autoWrap: 100
            x-maxDisplacement: 200
            x-goodnessOfFit: 0.8
            x-labelPriority: ${10-LABELRANK}
    
  2. Change the fill-color to the following CQL expression:

      rules:
         symbolizers:
         - polygon:
             stroke-color: '#777777'
             stroke-dasharray: '4 4'
             stroke-width: 0.5
             fill-color: ${
                 recode(MAPCOLOR7,
                   1, '#FFC3C3', 2, '#FFE3C3', 3, '#FFFFC3', 4, '#C3FFE3',
                   5, '#C3FFFF', 6, '#C3C3FF', 7, '#FFC3FF')
               }
             fill-opacity: 0.5
    

This sets the fill-color based on the value of MAPCOLOR7, according to the key-value pairs in the recode function: if MAPCOLOR7 = 1, set to '#FFC3C3', if MAPCOLOR7 = 2 set to '#FFE3E3', etc.

It should be noted that this will produce the exact same output as in the previous section.

Final style

The full style now looks like this:

name: countries
title: Countries style
abstract: countries of the world
feature-styles:
- name: name
  rules:
  - symbolizers:
     - polygon:
        stroke-color: '#777777'
        stroke-dasharray: '4 4'
        stroke-width: 0.5
        fill-color: ${
            recode(MAPCOLOR7,
              1, '#FFC3C3', 2, '#FFE3C3', 3, '#FFFFC3', 4, '#C3FFE3',
              5, '#C3FFFF', 6, '#C3C3FF', 7, '#FFC3FF')
          }
        fill-opacity: 0.5
  - symbolizers:
    - text:
        label: ${strToUpperCase(NAME)}
        font-size: 14
        font-family: SansSerif
        font-weight: bold
        fill-color: '#333333'
        x-autoWrap: 100
        x-maxDisplacement: 200
        x-goodnessOfFit: 0.8
        x-labelPriority: ${10-LABELRANK}

Continue on to Styling a line layer.