Creating Stunning Maps in GeoServer: mastering SLD and CSS styles

Various software can style maps and generate a proper SLD document for OGC compliant WMS like GeoServer to use. However, in most occasions, the styling allowed by the graphical tools is pretty limited and not good enough to achieve good looking, readable and efficient cartographic output. For those that like to write their own styles CSS also represents a nice alternatives thanks to its compactness and expressiveness.

Several topics will be covered, providing examples in both SLD and CSS for each, including: mastering multi-scale styling, using GeoServer extensions to build common hatch patterns, line styling beyond the basics, such as cased lines, controlling symbols along a line and the way they repeat, leveraging TTF symbol fonts and SVGs to generate good looking point thematic maps, using the full power of GeoServer label lay-outing tools to build pleasant, informative maps on both point, polygon and line layers, including adding road plates around labels, leverage the labeling subsystem conflict resolution engine to avoid overlaps in stand alone point symbology, blending charts into a map, dynamically transform data during rendering to get more explicative maps without the need to pre-process a large amount of views.

The presentation aims to provide the attendees with enough information to master SLD/CSS documents and most of GeoServer extensions to generate appealing, informative, readable maps that can be quickly rendered on screen.

Transcript

1. Creating stunning maps
   with GeoServer
   With SLD, CSS, YSLD and MBStyles
   Ing. Andrea Aime
   GeoSolutions
   1
   

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2. GeoSolutions
   ⚫
   Founded in Italy in late 2006
   ⚫
   Expertise
   • Image Processing, GeoSpatial Data Fusion
   • Java, Java Enterprise, C++, Python
   • JPEG2000, JPIP, Advanced 2D visualization
   ⚫
   Supporting/Developing FOSS4G projects
   ⚫
   GeoServer, MapStore
   ⚫
   GeoNetwork, GeoNode, Ckan
   ⚫
   Clients
   ⚫
   Public Agencies
   ⚫
   Private Companies
   ⚫
   http://www.geo-solutions.it
   2 FOSS4G 2018, August 29th/31st, Dar Es Salaam
   

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3. Quick tour of styling languages
   3
   

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4. Languages
   SLD 1.0
   core
   SLD 1.1
   core
   YSLD
   extension
   MBStyles
   community
   GeoCSS
   extension
   SLD 1.0
   inspired
   object
   model, with
   extensions
   parse
   parse
   parse
   parse
   and translate
   parse
   and translate
   4
   Map
   rendering
   FOSS4G 2018, August 29th/31st, Dar Es Salaam
   

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5. Shared concepts
   ⚫
   Layer (the styles applies to)
   ⚫
   Rules
   ⚫
   Filters/selectors (what should be painted)
   ⚫
   Scale dependencies (zoomed in, zoomed out?)
   ⚫
   Symbolizers (how should it be painted)
   ⚫
   Point
   ⚫
   Line
   ⚫
   Polygon
   ⚫
   Text
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6. Styled Layer Descriptor 1.0 and 11
   ⚫
   The only OGC standard
   ⚫
   XML based, verbose, hard to hand edit,
   was meant for machine export but ended
   up being edited a lot by hand
   ⚫
   Can be generated by external tools and
   imported
   ⚫
   However interoperability is limited
   ⚫
   Often needs to be hand tweaked
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7. SLD 1.0 example
   
   …
   
   
   
   type
   alpine_hut
   
   
   100000.0
   
   
   
   xlink:type="simple"
   xlink:href="symbols/alpinehut.p.16.png"/>
   image/png
   
   
   
   
   
   Filter
   Scale dep.
   Symbolizer
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8. YSLD
   ⚫
   SLD in YAML syntax
   ⚫
   Filtering by CQL
   ⚫
   Can define reusable variables and blocks
   ⚫
   Verbosity it’s between SLD and CSS
   ⚫
   Has a notion of zoom levels, if needed
   feature-styles:
   - rules:
   - filter: type = 'alpine_hut'
   scale: (,100000.0)
   symbolizers:
   - point:
   symbols:
   - external:
   url: symbols/alpinehut.p.16.png
   format: image/png
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9. GeoCSS
   ⚫
   Compact syntax, familiar for web developers
   ⚫
   CQL based filtering, rule nesting and cascading
   keeps complex styling compact (you just
   express the overrides to the base)
   ⚫
   The only style language with auto-complete in
   the style editor
   ⚫
   Does not get any more compact than this:
   ⚫
   Cons: some are confused by “rule cascading”
   [type = 'alpine_hut'][@sd < 100k] {
   mark: url('symbols/alpinehut.p.16.png');
   }
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10. MBStyles (aka MapBox GL)
    ⚫
    Whole different beast
    ⚫
    JSON based, designed for GUI editing (like
    SLD) instead of hand editing
    ⚫
    Only zoom level based scale control
    ⚫
    Symbols coming from “sprites” (symbol
    collections)
    ⚫
    Pro: can be applied both on the client side and
    the server side
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11. MBStyles (aka MapBox GL)
    {
    "version": 8,
    … boilerplate omitted here
    "name": "mountain huts",
    "sprite": "https://my.sever/sprite",
    "layers": [
    {
    "id": "huts",
    "type": "symbol",
    "minzoom": 9,
    "filter": [
    "==",
    "type",
    "alpine_hut"
    ],
    "layout": {
    "icon-image": "alpinehut",
    "icon-size": 1,
    "icon-allow-overlap": true
    }
    }
    ]
    }
    Filter (in postfix notation!)
    Scale dep.
    Symbolizer
    The sprint contains various images,
    like in videogames
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12. What’s next
    ⚫
    Going to explore styling concepts
    ⚫
    Languages used in examples
    ⚫
    SLD 1.0 + GS extensions
    ⚫
    YSLD
    ⚫
    GeoCSS
    YSLD
    SLD
    CSS
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13. Scale dependencies
    13
    

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14. Types of Scale dependency
    ⚫
    Decide whether to symbolize based on the scale or not
    ⚫
    E.g., at lower scales/lower zoom levels do not show buildings
    ⚫
    Symbolize in a different way depending on the scale
    ⚫
    E.g., different thickness based on the current zoom
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15. Expressing scale dependency filters
    ⚫
    SLD:
    ⚫
    
    1000
    
    ⚫
    
    1000000
    
    ⚫
    CSS
    ⚫
    [@sd > 1k][@sd < 1M]
    ⚫
    Compact expression of large numbers makes them
    readable at a glance, e.g., 100k, 1M
    ⚫
    YSLD:
    ⚫
    scale: (1000, 1000000)
    ⚫
    scale: (1e3, 1e6)
    ⚫
    zoom: (8, 16)
    grid:
    name: WGS84
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16. Unit of Measure
    ⚫
    Useful if you have real world measures of line
    thicknesses and the like
    …
    
    
    #0000FF
    5
    
    
    ...
    …
    stroke: blue;
    stroke-width: 5m;
    …
    line:
    stroke-color: '#0000FF'
    uom: metre;
    stroke-width: '5';
    SLD
    YSLD
    CSS
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17. Transformation functions
    ⚫
    Another way of setting a different value
    depending on the current scale/zoom level
    ⚫
    Useful if the scaling is not linear
    [class = 'highway’
    and type in ('motorway’,
    'motorway_link’)]
    [@sd < 25M] {
    stroke: #e66e89;
    stroke-width: categorize(@sd,
    2, 400k,
    1.9, 800k,
    1.4, 1.5M,
    1, 3M,
    0.8, 6M,
    0.5);
    ⚫
    Less than 400k → 2px
    ⚫
    [400k, 800k] → 1.9px
    ⚫
    [800k, 1.5M] → 1.4px
    ⚫
    [1.5M, 3M] → 1
    ⚫
    [3M, 6M] → 0.8
    ⚫
    Above 6M -> 0.5
    CSS
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18. Transformation functions in SLD
    
    
    #e66e89
    
    
    
    wms_scale_denominator
    
    2
    400000
    1.9
    800000
    1.4
    1500000
    1
    3000000
    0.8
    6000000
    0.5
    
    
    
    
    SLD
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19. Point styling
    19
    

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20. Simple image
    [type = 'alpine_hut'][@sd < 100k] {
    mark: url('symbols/alpinehut.p.16.png');
    }
    
    
    
    type
    alpine_hut
    
    
    100000.0
    
    
    
    xlink:type="simple"
    xlink:href="symbols/alpinehut.p.16.png"/>
    image/png
    
    
    
    
    SLD
    CSS
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21. Marks (SVG in this case)
    [type = 'bank'][@sd < 6k] {
    mark: symbol('file://symbols/bank.svg');
    :mark { fill: #734a08 };
    mark-size: 14;
    }
    feature-styles:
    - rules:
    - filter: type = 'bank'
    scale: (,6000.0)
    symbolizers:
    - point:
    symbols:
    - mark:
    shape: file://symbols/bank.svg
    fill-color: ! '#734a08'
    size: 14 YSLD
    CSS
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22. Marks composition and override
    [type = 'fountain’] {
    [@sd < 6k] {
    mark: symbol(circle), symbol(circle);
    :nth-mark(1) { fill: #b5d0d0 };
    :nth-mark(2) { fill: #576ddf };
    mark-size: 10, 3;
    };
    [@sd < 3k] {
    mark: symbol('file://symbols/fountain.svg');
    :mark { fill: #576ddf; };
    }
    }
    CSS
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23. ⚫
    Many other options!
    ⚫
    Built-in symbol names (well known marks): circle,
    square, triangle, …
    ⚫
    From TTF fonts using the name
    ttf://#charcode
    ⚫
    Windbarbs, e.g.:
    windbarbs://default(15)[kts]
    ⚫
    WKT specification, e.g.
    wkt://MULTILINESTRING((-0.25 -0.25, -0.125 -0.25), (0.125 -
    0.25, 0.25 -0.25), (-0.25 0.25, -0.125 0.25), (0.125 0.25, 0.25
    0.25))
    ⚫
    See more here:
    http://docs.geoserver.org/latest/en/user/styling/sld/exte
    nsions/pointsymbols.html
    Other mark options
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24. Filling polygons
    24
    

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25. Solid filling
    * {
    fill: lightgrey;
    stroke: black;
    stroke-width: 0.5;
    }
    
    
    #d3d3d3
    
    
    0.5
    
    SLD
    CSS
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26. Filling with repeating images
    fill
    [@sd < 800k][type in ('cemetery', 'grave_yard')] {
    fill: #aacbaf;
    [@sd < 50k] {
    [religion = 'jewish'] {
    fill: #aacbaf, url('symbols/grave_yard_jewish.png');
    };
    [religion = 'christian'] {
    fill: #aacbaf, url('symbols/grave_yard_christian.png');
    };
    [religion = 'INT-generic'] {
    fill: #aacbaf, url('symbols/grave_yard_generic.png');
    };
    };
    } CSS
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27. Filling with repeating images (YSLD)
    feature-styles:
    - rules:
    - filter: type IN ('cemetery','grave_yard')
    scale: (,800000.0)
    symbolizers:
    - polygon:
    fill-color: ! '#aacbaf'
    - filter: (type IN ('cemetery','grave_yard')) AND religion =
    'jewish'
    scale: (,50000.0)
    symbolizers:
    - polygon:
    fill-graphic:
    symbols:
    - external:
    url: symbols/grave_yard_jewish.png
    format: image/png
    # continues in the next slide
    First uniform background fill
    Then foreground symbols for
    various religions
    YSLD
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28. Filling with repeating images (YSLD)
    - filter: (type IN ('cemetery','grave_yard')) AND religion =
    'christian'
    scale: (,50000.0)
    symbolizers:
    - polygon:
    fill-graphic:
    symbols:
    - external:
    url: symbols/grave_yard_christian.png
    format: image/png
    - filter: (type IN ('cemetery','grave_yard')) AND religion =
    'INT-generic'
    scale: (,50000.0)
    symbolizers:
    - polygon:
    fill-graphic:
    symbols:
    - external:
    url: symbols/grave_yard_generic.png
    format: image/png YSLD
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29. Hatching
    
    
    
    
    
    shape://times
    
    #ADD8E6
    
    
    8
    
    
    
    
    
    [@scale < 10000] {
    fill: symbol('shape://times');
    fill-size: 8;
    :fill {
    stroke: #ADD8E6;
    }
    }
    SLD
    CSS
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30. Painting lines
    30
    

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31. Solid lines (OSM admin borders)
    [type = 'administrative'] {
    [admin_level <= 4],
    [admin_level = 5 or admin_level = 6][@sd <= 400k],
    [admin_level = 7 or admin_level = 8][@sd <= 200k],
    [admin_level = 9 or admin_level = 10][@sd <= 100k] {
    stroke: #ac46ac;
    stroke-opacity: 0.4;
    }
    }
    CSS
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32. Dashes
    …
    
    
    #6B4900
    0.1
    2 2
    
    
    …
    stroke: #6B4900;
    stroke-width: 0.1;
    stroke-dasharray: 2 2;
    …
    SLD
    CSS
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33. Alternating dashes with marks
    * {
    stroke: darkRed, symbol('circle');
    stroke-dasharray: 10 14, 6 18;
    stroke-dashoffset: 14, 0;
    :stroke {
    fill: darkRed;
    size: 6;
    }
    }
    ⚫
    Two coordinated dashed lines
    ⚫
    One made with lines
    ⚫
    One made with circles
    ⚫
    The offset shifts them to have
    one appear in the empty
    spaces of the other
    CSS
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34. Labeling
    34
    

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35. Vendor options
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36. Point labels and obstacles
    [@sd < 200k] {
    label: [FULLNAME];
    label-anchor: 0.5 1.0;
    label-offset: 0.0 -14.0;
    font-fill: #000033;
    font-family: Arial;
    font-size: 12;
    halo-color: white;
    halo-radius: 1.5;
    label-priority: 200000;
    label-auto-wrap: 100;
    mark: url('./img/landmarks/${IMAGE}’);
    mark-label-obstacle: true;
    }
    «FULLNAME»
    attribute
    Auto wrapping
    label with halo.
    Data driven
    symbol URL
    Labels won’t overlap
    the symbol
    CSS
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37. Line labels
    [@sd < 200k] {
    label: [LABEL_NAME];
    font-fill: #000000;
    font-family: Arial;
    font-size: 13;
    font-style: normal;
    font-weight: bold;
    halo-color: #FFFFFF;
    halo-radius: 1;
    label-follow-line: true;
    label-repeat: 400;
    label-group: true;
    label-max-displacement: 200;
    }
    Draw «LABEL_NAME»,
    black, with white halo
    Draw them along lines,
    fuse segments with
    same label, repeat
    CSS
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38. Polygon labels
    
    
    FULLNAME
    
    
    Arial
    14.0
    bold
    
    
    
    
    0.5
    0.5
    
    
    
    
    #000000
    
    50000
    100
    200
    0.9
    
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39. Raster styling
    39
    

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40. A DEM and a color map
    ⚫
    SRTM from USGS
    ⚫
    Standard color map
    ⚫
    In 2.14.x we’ll also be able
    to add shaded relief (not
    shown here)
    [@sd > 75000] {
    raster-channels: auto;
    raster-color-map:
    color-map-entry(#00BFBF, -100.0, 0)
    color-map-entry(#00FF00, 920.0, 0)
    color-map-entry(#00FF00, 920.0, 1.0)
    color-map-entry(#FFFF00, 1940.0, 1.0)
    color-map-entry(#FFFF00, 1940.0, 1.0)
    color-map-entry(#FF7F00, 2960.0, 1.0)
    color-map-entry(#FF7F00, 2960.0, 1.0)
    color-map-entry(#BF7F3F, 3980.0, 1.0)
    color-map-entry(#BF7F3F, 3980.0, 1.0)
    color-map-entry(#141514, 5000.0, 1.0);
    }
    CSS
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41. Contrast enhancement
    http://docs.geoserver.org/latest/en/user/styling/sld-
    reference/rastersymbolizer.html#contrastenhancement
    
    
    
    
    StretchToMinimumMaximum
    
    50
    800
    
    
    
    GeoServer
    vendor extension
    SLD
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42. Other assorted features
    42
    

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43. Color blending and alpha compositing
    http://docs.geoserver.org/stable/user/styling/sld-extensions/composite-blend/index.html
    More info
    at:
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44. Z ordering
    http://docs.geoserver.org/latest/en/user/styling/sld-
    extensions/z-order/example.html
    [class = 'motorways'] {
    stroke: #990000, #ff6666;
    stroke-width: 8, 6;
    stroke-linecap: round;
    z-index: 0, 3;
    }
    [class = 'railways'] {
    stroke: #333333;
    stroke-width: 3;
    z-index: 2;
    }
    [class = 'railways'] {
    stroke: #ffffff;
    stroke-width: 1.5;
    stroke-dasharray: 5 5;
    z-index: 3;
    }
    * {
    sort-by: "z_order";
    sort-by-group:
    "roadsGroup";
    } CSS
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45. Geometry transformations
    [@scale < 10000] {
    fill-geometry: [offset(the_geom, 6, -6)];
    fill: darkgray;
    z-index: 0;
    }
    [@scale < 10000] {
    fill: #b3b3b3;
    z-index: 1;
    } CSS
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46. Rendering transformations
    * {
    transform: ras:Contour(levels:
    1100 1200 1300 1400
    1500 1600 1700 1800);
    stroke: black;
    label: [GRAY-INDEX];
    font-fill: black;
    font-family: Sans;
    font-size: 12;
    halo-radius: 2;
    halo-color: white;
    label-follow-line: true
    } CSS
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47. New transform in 2.14: map algebra
    * {
    transform: ras:Jiffle(script:
    ‘ nir = src[7];
    vir = src[3];
    dest = (nir-vir)/(nir+vir);’);
    raster-channels: auto;
    raster-color-map:
    color-map-entry(#00BFBF, -100.0, 0)
    color-map-entry(#00FF00, 920.0, 0)
    …
    } CSS
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48. QGIS export
    48
    

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49. QGIS SLD export work
    ⚫
    In QGIS 2.18, Bonn code sprint improvements
    ⚫
    In QGIS 3.0 support for label exports (thanks for
    OpenGeoGroep sponsoring)
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50. More to come
    ⚫
    OSGeo UK sponsorship
    ⚫
    The GeoServer PSC looks for proposals
    ⚫
    E.g., we could have basic raster symbolizer
    export
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51. That’s all folks!
    Questions?
    info@geo-solutions.it
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