Creating Maps in GeoServer using CSS and SLD (FOSS4G 2022 Edition)

The presentation aims to provide attendees with enough information to master GeoServer styling documents and most of GeoServer extensions to generate appealing, informative, readable maps that can be quickly rendered on screen. Examples will be provided from GeoSolutions training material, as well as from the OSM data directory we shared with the community.

Several topics will be covered, providing examples in CSS and SLD, including:
- Mastering common symbolization, filtering, multi-scale styling.
- Using GeoServer extensions to build common hatch patterns, line styling beyond the basics, 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.
- Dynamically transform data during rendering to get more explicative maps without the need to pre-process a large amount of views.
- Generating styles with external tools.

Transcript

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

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2. GeoSolutions
   Enterprise Support
   Services
   Deployment
   Subscription
   Professional
   Training
   Customized
   Solutions
   GeoNode
   • Offices in Italy & US, Global Clients/Team
   • 40+ collaborators, 30+ Engineers
   • Our products
   • Our Offer
   

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3. Affiliations
   We strongly support Open
   Source, it Is in our core
   We actively participate in
   OGC working groups and
   get funded to advance new
   open standards
   We support standards
   critical to GEOINT
   

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4. Quick tour of styling languages
   4
   

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5. 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
   5
   Map
   rendering
   

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6. Shared concepts
   ●
   Layers (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
   6
   

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7. Styled Layer Descriptor 1.0 and 11
   ●
   OGC styling standard, XML based
   ●
   Was meant for machine export but ended
   up being edited a lot by hand
   ●
   Can be generated by external tools and
   imported (with some hand tweaking)
   7
   

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8. 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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9. 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
   9
   

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10. GeoCSS
    ●
    Compact syntax, familiar for web developers
    ●
    CQL based filtering, rule nesting and cascading
    keeps styling compact
    ●
    Does not get any more compact than this:
    ●
    Cons: some are confused by “rule cascading”
    🡪 can now be turned off
    [type = 'alpine_hut'][@sd < 100k] {
    mark: url('symbols/alpinehut.p.16.png');
    }
    10
    

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11. MBStyles (aka MapBox GL)
    ●
    Symbols as “sprites”
    (symbol collections)
    ●
    Can be applied both
    on the client side and
    the server side
    ●
    Online editors
    available, complex
    expressions still
    require writing JSON
    ●
    JSON based, designed for GUI editing (like
    SLD) instead of hand editing
    ●
    Scale control based only on Web Mercator
    zoom levels
    ●
    

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12. 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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13. Styling concepts:
    Scale dependencies
    13
    

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14. 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 , 10M
    Show buildings
    as user zooms
    in
    

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15. Unit of Measure
    ●
    Real world measures, sizes grow as one zooms
    in
    …
    
    
    #0000FF
    5
    
    
    ...
    …
    stroke: blue;
    stroke-width: 5m;
    SLD
    CSS
    

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16. Transformation functions
    ●
    Use a different value depending on the current
    scale/zoom level
    ●
    For non linear scaling
    [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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17. 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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18. Point styling
    18
    

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19. Simple symbol
    [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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20. SVG as a scalable, fillable shape
    [type = 'bank'][@sd < 6k] {
    mark: symbol('file://symbols/bank.svg');
    :mark { fill: #734a08 };
    mark-size: 14;
    }
    
    
    
    type
    bank
    
    
    6000
    
    
    
    file://symbols/bank.svg
    
    #734a08
    
    
    14
    
    
    
    CSS
    bank.svg
    

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21. 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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22. ●
    Here are some examples:
    ●
    From TTF fonts using the name
    ttf://#charcode
    ●
    Windbarbs, e.g.:
    windbarbs://default(15)[kts]
    ●
    WKT specification, e.g.
    wkt://MULTIPOLYGON(((-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)
    …… )
    ●
    Build your own, pluggable system
    ●
    Full docs at:
    http://docs.geoserver.org/latest/en/user/styling/sld/exte
    nsions/pointsymbols.html
    Other mark options
    

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23. Filling polygons
    23
    

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24. Solid filling
    * {
    fill: lightgrey;
    stroke-width: 0.5;
    }
    
    
    #d3d3d3
    
    
    0.5
    
    SLD
    CSS
    

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25. Overlap solid fills with repeated icons
    fill
    [@sd < 800k][type in ('cemetery', 'grave_yard')] {
    fill: #aacbaf;
    [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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26. Hatching
    
    
    
    
    
    shape://times
    
    #ADD8E6
    
    
    8
    
    
    
    
    
    [@scale < 10000] {
    fill: symbol('shape://times');
    fill-size: 8;
    :fill {
    stroke: #ADD8E6;
    }
    }
    SLD
    CSS
    

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27. Line symbology
    27
    

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28. 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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29. Dashes/Marks/images along a line
    * {
    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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30. Labeling
    30
    

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31. Vendor options
    • Priority labelling, static or attribute based
    • Deluge of vendor options to control in detail labelling:
    • group
    • labelAllGroup
    • spaceAround
    • followLine
    • maxDisplacement
    • repeat
    • maxAngleDelta
    • autoWrap
    • forceLeftToRight
    • conflictResolution
    • goodnessOfFit
    • polygonAlign
    • graphic-resize
    • graphic-margin
    • partials
    • underlineText
    • strikethroughText
    • charSpacing
    • wordSpacing
    

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32. Polygon labels
    
    
    FULLNAME
    
    
    Arial
    14.0
    bold
    
    
    
    
    0.5
    0.5
    
    
    
    
    #000000
    
    50000
    100
    200
    0.9
    
    SLD
    

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33. 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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34. 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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35. Raster styling
    35
    

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36. A DEM and a color map
    ●
    SRTM from USGS
    ●
    Standard color map
    ●
    Also shaded relief (not
    shown in the css below)
    [@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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37. 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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38. Other assorted features
    38
    

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39. Color blending and alpha compositing
    multiply color-burn difference
    Source Destination
    https://docs.geoserver.org/latest/en/user/styling/sld/extensions/composite-blend/index.html
    More info at:
    Mask with alpha compositing
    
    multiply, 0.5
    
    

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40. Z ordering
    https://docs.geoserver.org/latest/en/user/styling/sl
    d/extensions/z-order/syntax.html#z-ordering-acros
    s-layers
    [class = 'motorways'] {
    stroke: #990000, #ff6666;
    stroke-width: 8, 6;
    stroke-linecap: round;
    z-index: 0, 2;
    }
    [class = 'railways'] {
    stroke: #333333;
    stroke-width: 3;
    z-index: 1;
    }
    [class = 'railways'] {
    stroke: #ffffff;
    stroke-width: 1.5;
    stroke-dasharray: 5 5;
    z-index: 2;
    }
    * {
    sort-by: "z_order";
    sort-by-group:
    "roadsGroup";
    } CSS
    40
    

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41. Rendering transformations
    • WPS + WMS +
    rendering optimizations
    • In this slide, on the fly
    contour extraction
    * {
    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
    41
    

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42. Jiffle 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
    On the fly NDVI
    computation
    from Sentinel 2
    images
    

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43. Point and click editors
    43
    

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44. QGIS SLD export
    • Basic vector and raster
    styling covered
    • Much advanced bits missing
    though
    • Needs sponsoring on both ends
    (QGIS and GeoServer)
    

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45. GeoStyler
    https://geostyler.github.io/geostyler-demo/
    

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46. MapStore styler
    https://mapstore.readthedocs.io/en/latest/user-guide/layer-settings/#visual-editor-style
    

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47. That’s all folks!
    Questions?
    info@geosolutionsgroup.com
    47
    

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