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.

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

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
FOSS4G 2017, Boston
August 14th-19th 2017

3. SLD vs CSS
 Styled Layer Descriptor
 OGC standard
 XML based, verbose, hard to hand edit
 Only showing relevant bits of the SLD
 GeoCSS
 CSS with extensions for map rendering
 Simple, Compact, designed for human beings
 Not a standard (several incompatible variants for
mapping, GeoServer one has nothing to do with
CartoDB/MapBox one)
FOSS4G 2017, Boston
August 14th-19th 2017

4. CSS features
 Familiar for web developers
 Compact syntax
 Symbolization triggered by “key” properties
(stroke, fill, mark, label, channel-selection)
 CQL based filtering
 Cascading keeps complex styling compact (you
just express the overrides to the base)
 Interactive editor for productive style
development
FOSS4G 2017, Boston
August 14th-19th 2017

5. GeoCSS in a nutshell
• Filter by attribute/env variable in CQL
• Filter by scale
• Set properties to control symbolization
• Key properties activate certain symbolization:
– mark/fill/stroke/label/raster-channels
FOSS4G 2017, Boston
August 14th-19th 2017
[admin_level < 2][@sd < 1M][@sd > 100k] {
label: name;
font-family: ‘Noto Sans’;
…
/* this is nested rule */
[special = true][@sd < 500k] {
font-weight: bold;
…
}
}

6. SLD equivalents
FOSS4G 2017, Boston
August 14th-19th 2017
<sld:Rule>
<ogc:Filter>
<ogc:PropertyIsEqualTo>
<ogc:PropertyName>admin_level</ogc:PropertyName>
<ogc:Literal>2</ogc:Literal>
</ogc:PropertyIsEqualTo>
</ogc:Filter>
<sld:MinScaleDenominator>100000</sld:MinScaleDenominator>
<sld:MaxScaleDenominator>1000000</sld:MaxScaleDenominator>
<sld:TextSymbolizer>
<sld:Label>
<ogc:PropertyName>name</ogc:PropertyName>
</sld:Label>
<sld:Font>
<sld:CssParameter name="font-family">
Noto Sans
</sld:CssParameter>
<sld:CssParameter name="font-size">10
...
</sld:TextSymbolizer>
<!–- Override would require a separate rule specifying everything again -->
</sld:Rule>
Filter
Scale
dependency
Symbolizers
and their
properties

7. Scale dependencies
FOSS4G 2017, Boston
August 14th-19th 2017

8. 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
FOSS4G 2017, Boston
August 14th-19th 2017

9. Expressing scale dependency filters
 SLD:
 <MinScaleDenominator>
 <MaxScaleDenominator>
 CSS
 Legacy: [@scale > 10000000]
 GeoServer 2.12+: [@sd > 1M]
 More compact variable, more correct (it’s a scale
denominator, not a scale!)
 Compact expression of large numbers makes them readable
at a glance, e.g., 100k, 1M
FOSS4G 2017, Boston
August 14th-19th 2017

10. Unit of Measure
FOSS4G 2017, Boston
August 14th-19th 2017
 Useful if you have real world measures of line
thicknesses and the like
<LineSymbolizer uom="http://www.opengeospatial.org/se/units/metre">
<Stroke>
<CssParameter name="stroke">#0000FF</CssParameter>
<CssParameter name="stroke-width">5</CssParameter>
</Stroke>
</LineSymbolizer>
* {
stroke: blue;
stroke-width: 5m;
}

11. Transformation functions
FOSS4G 2017, Boston
August 14th-19th 2017
 OSM like, setting a different value depending on
the current scale/zoom level
 Not a linear scale mind
[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

12. Transformation functions in SLD
FOSS4G 2017, Boston
August 14th-19th 2017
<sld:LineSymbolizer>
<sld:Stroke>
<sld:CssParameter name="stroke">#e66e89</sld:CssParameter>
<sld:CssParameter name="stroke-width">
<ogc:Function name="Categorize">
<ogc:Function name="env">
<ogc:Literal>wms_scale_denominator</ogc:Literal>
</ogc:Function>
<ogc:Literal>2</ogc:Literal>
<ogc:Literal>400000</ogc:Literal>
<ogc:Literal>1.9</ogc:Literal>
<ogc:Literal>800000</ogc:Literal>
<ogc:Literal>1.4</ogc:Literal>
<ogc:Literal>1500000</ogc:Literal>
<ogc:Literal>1</ogc:Literal>
<ogc:Literal>3000000</ogc:Literal>
<ogc:Literal>0.8</ogc:Literal>
<ogc:Literal>6000000</ogc:Literal>
<ogc:Literal>0.5</ogc:Literal>
</ogc:Function>
</sld:CssParameter>
</sld:Stroke>
</sld:LineSymbolizer>

13. Point styling
FOSS4G 2017, Boston
August 14th-19th 2017

14. Simple symbol
FOSS4G 2017, Boston
August 14th-19th 2017
[type = 'alpine_hut'][@sd < 100k] {
mark: url('symbols/alpinehut.p.16.png');
}
<sld:Rule>
<ogc:Filter>
<ogc:PropertyIsEqualTo>
<ogc:PropertyName>type</ogc:PropertyName>
<ogc:Literal>alpine_hut</ogc:Literal>
</ogc:PropertyIsEqualTo>
</ogc:Filter>
<sld:MaxScaleDenominator>100000.0</sld:MaxScaleDenominator>
<sld:PointSymbolizer>
<sld:Graphic>
<sld:ExternalGraphic>
<sld:OnlineResource xmlns:xlink="http://www.w3.org/1999/xlink"
xlink:type="simple"
xlink:href="symbols/alpinehut.p.16.png"/>
<sld:Format>image/png</sld:Format>
</sld:ExternalGraphic>
</sld:Graphic>
</sld:PointSymbolizer>
</sld:Rule>

15. Marks (SVG in this case)
FOSS4G 2017, Boston
August 14th-19th 2017
[type = 'bank'][@sd < 6k] {
mark: symbol('file://symbols/bank.svg');
:mark { fill: #734a08 };
mark-size: 14;
}
<sld:Rule>
<ogc:Filter>
<ogc:PropertyIsEqualTo>
<ogc:PropertyName>type</ogc:PropertyName>
<ogc:Literal>bank</ogc:Literal>
</ogc:PropertyIsEqualTo>
</ogc:Filter>
<sld:MaxScaleDenominator>6000.0</sld:MaxScaleDenominator>
<sld:PointSymbolizer>
<sld:Graphic>
<sld:Mark>
<sld:WellKnownName>file://symbols/bank.svg</sld:WellKnownName>
<sld:Fill>
<sld:CssParameter name="fill">#734a08</sld:CssParameter>
</sld:Fill>
</sld:Mark>
<sld:Size>14</sld:Size>
</sld:Graphic>
</sld:PointSymbolizer>
</sld:Rule>
New in
GeoServer
2.12!

16. Marks composition and override
FOSS4G 2017, Boston
August 14th-19th 2017
[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; };
}
}

17.  Many other options!
 Built-in symbol names (well known marks): circle,
square, triangle, …
 From TTF fonts using the name
ttf://<fontname>#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
FOSS4G 2017, Boston
August 14th-19th 2017

18. Filling polygons
FOSS4G 2017, Boston
August 14th-19th 2017

19. Solid filling
FOSS4G 2017, Boston
August 14th-19th 2017
* {
fill: lightgrey;
stroke: black;
stroke-width: 0.5;
}
<sld:PolygonSymbolizer>
<sld:Fill>
<sld:CssParameter name="fill">#d3d3d3</sld:CssParameter>
</sld:Fill>
<sld:Stroke>
<sld:CssParameter name="stroke-width">0.5</sld:CssParameter>
</sld:Stroke>
</sld:PolygonSymbolizer>

20. Filling with repeating images
fill
FOSS4G 2017, Boston
August 14th-19th 2017
[@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');
};
};
}

21. Filling with repeating images (SLD)
FOSS4G 2017, Boston
August 14th-19th 2017
<sld:Rule>
<ogc:Filter>
<ogc:And>
<ogc:Or>
<ogc:PropertyIsEqualTo>
<ogc:PropertyName>type</ogc:PropertyName>
<ogc:Literal>cemetery</ogc:Literal>
</ogc:PropertyIsEqualTo>
<ogc:PropertyIsEqualTo>
<ogc:PropertyName>type</ogc:PropertyName>
<ogc:Literal>grave_yard</ogc:Literal>
</ogc:PropertyIsEqualTo>
</ogc:Or>
<ogc:PropertyIsEqualTo>
<ogc:PropertyName>religion</ogc:PropertyName>
<ogc:Literal>jewish</ogc:Literal>
</ogc:PropertyIsEqualTo>
</ogc:And>
</ogc:Filter>
<sld:MaxScaleDenominator>50000.0</sld:MaxScaleDenominator>
One sample rule (the Jewish religion one).
Three more needed to get the same
display as with CSS

22. Filling with repeating images (SLD)
FOSS4G 2017, Boston
August 14th-19th 2017
<sld:PolygonSymbolizer>
<sld:Fill>
<sld:CssParameter name="fill">#aacbaf</sld:CssParameter>
</sld:Fill>
</sld:PolygonSymbolizer>
<sld:PolygonSymbolizer>
<sld:Fill>
<sld:GraphicFill>
<sld:Graphic>
<sld:ExternalGraphic>
<sld:OnlineResource
xmlns:xlink="http://www.w3.org/1999/xlink"
xlink:type="simple"
xlink:href="symbols/grave_yard_jewish.png" />
<sld:Format>image/png</sld:Format>
</sld:ExternalGraphic>
</sld:Graphic>
</sld:GraphicFill>
</sld:Fill>
</sld:PolygonSymbolizer>
</sld:Rule>

23. Filling with marks
FOSS4G 2017, Boston
August 14th-19th 2017
<sld:PolygonSymbolizer>
<sld:Fill>
<sld:GraphicFill>
<sld:Graphic>
<sld:Mark>
<sld:WellKnownName>shape://times</sld:WellKnownName>
<sld:Stroke>
<sld:CssParameter name="stroke">#ADD8E6</sld:CssParameter>
</sld:Stroke>
</sld:Mark>
<sld:Size>8</sld:Size>
</sld:Graphic>
</sld:GraphicFill>
</sld:Fill>
</sld:PolygonSymbolizer>
</sld:Rule>
[@scale < 10000] {
fill: symbol('shape://times');
fill-size: 8;
:fill {
stroke: #ADD8E6;
}
}

24. Painting lines
FOSS4G 2017, Boston
August 14th-19th 2017

25. Solid lines (OSM admin borders)
FOSS4G 2017, Boston
August 14th-19th 2017
[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;
}
}
<!-- 5 different rules with different filters followed by this -->
<sld:LineSymbolizer>
<sld:Stroke>
<sld:CssParameter name="stroke">#ac46ac</sld:CssParameter>
<sld:CssParameter name="stroke-opacity">0.4</sld:CssParameter>
</sld:Stroke>
</sld:LineSymbolizer>

26. Dashes
FOSS4G 2017, Boston
August 14th-19th 2017
…
<sld:LineSymbolizer>
<sld:Stroke>
<sld:CssParameter name="stroke">#6B4900</sld:CssParameter>
<sld:CssParameter name="stroke-width">0.1</sld:CssParameter>
<sld:CssParameter name="stroke-dasharray">2 2</sld:CssParameter>
</sld:Stroke>
</sld:LineSymbolizer>
[@sd < 75k] {
stroke: #6B4900;
stroke-width: 0.1;
stroke-dasharray: 2;
}

27. Alternating dashes with marks
FOSS4G 2017, Boston
August 14th-19th 2017
* {
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

28. Labeling
FOSS4G 2017, Boston
August 14th-19th 2017

29. Vendor options
FOSS4G 2017, Boston
August 14th-19th 2017

30. Point labels and obstacles
FOSS4G 2017, Boston
August 14th-19th 2017
[@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 URLLabels won’t overlap
the symbol

31. Line labels
FOSS4G 2017, Boston
August 14th-19th 2017
[@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

32. Polygon labels
FOSS4G 2017, Boston
August 14th-19th 2017
<sld:TextSymbolizer>
<sld:Label>
<ogc:PropertyName>FULLNAME</ogc:PropertyName>
</sld:Label>
<sld:Font>
<sld:CssParameter name="font-family">Arial</sld:CssParameter>
<sld:CssParameter name="font-size">14.0</sld:CssParameter>
<sld:CssParameter name="font-weight">bold</sld:CssParameter>
</sld:Font>
<sld:LabelPlacement>
<sld:PointPlacement>
<sld:AnchorPoint>
<sld:AnchorPointX>0.5</sld:AnchorPointX>
<sld:AnchorPointY>0.5</sld:AnchorPointY>
</sld:AnchorPoint>
</sld:PointPlacement>
</sld:LabelPlacement>
<sld:Fill>
<sld:CssParameter name="fill">#000000</sld:CssParameter>
</sld:Fill>
<sld:Priority>50000</sld:Priority>
<sld:VendorOption name="autoWrap">100</sld:VendorOption>
<sld:VendorOption name="maxDisplacement">200</sld:VendorOption>
<sld:VendorOption name="goodnessOfFit">0.9</sld:VendorOption>
</sld:TextSymbolizer>

33. Support for pre-laid-out labels
FOSS4G 2017, Boston
August 14th-19th 2017

34. Raster styling
FOSS4G 2017, Boston
August 14th-19th 2017

35. A DEM and a color map
FOSS4G 2016, Bonn
24nd – 24th August 2016
 SRTM from USGS
 Standard color map
 No-data natively
transparent in 2.8.x
thanks to JAI-EXT
[@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);
}

36. Contrast enhancement
http://docs.geoserver.org/latest/en/user/styling/sld-
reference/rastersymbolizer.html#contrastenhancement
FOSS4G 2017, Boston
August 14th-19th 2017
<sld:RasterSymbolizer>
<sld:ContrastEnhancement>
<sld:Normalize>
<sld:VendorOption name="algorithm">
StretchToMinimumMaximum
</sld:VendorOption>
<sld:VendorOption name="minValue">50</sld:VendorOption>
<sld:VendorOption name="maxValue">800</sld:VendorOption>
</sld:Normalize>
</sld:ContrastEnhancement>
</sld:RasterSymbolizer>
GeoServer
vendor extension

37. Other assorted features
FOSS4G 2017, Boston
August 14th-19th 2017

38. Geometry transformations
FOSS4G 2017, Boston
August 14th-19th 2017
[@scale < 10000] {
fill-geometry: [offset(the_geom, 6, -6)];
fill: darkgray;
z-index: 0;
}
[@scale < 10000] {
fill: #b3b3b3;
z-index: 1;
}

39. Rendering transformations
FOSS4G 2017, Boston
August 14th-19th 2017
* {
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
}

40. Masking via alpha compositing
FOSS4G 2016, Bonn
24nd – 24th August 2016
destination-in

41. Color blendin
FOSS4G 2017, Boston
August 14th-19th 2017
http://docs.geoserver.org/stable/user/styling/sld-extensions/composite-blend/index.html
More info at:

42. Z ordering
http://docs.geoserver.org/latest/en/user/styling/sld-
extensions/z-order/example.html
FOSS4G 2017, Boston
August 14th-19th 2017
[class = 'motorways'] {
stroke: #990000;
stroke-width: 8;
z-index: 0;
}
[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;
}
[class = 'motorways'] {
stroke: #ff6666;
stroke-width: 6;
stroke-linecap: round;
z-index: 3;
}
* {
sort-by: "z_order";
sort-by-group: "roadsGroup";
}

43. New in 2.12
FOSS4G 2017, Boston
August 14th-19th 2017

44. Autocomplete for CSS editor
 Because there are too many properties to
remember!
FOSS4G 2017, Boston
August 14th-19th 2017

45. No more -gt- prefix in CSS
 Vendor options used to be prefixed with “-gt-”
 But CSS is its own language, no need to mark
something as “vendor” or refer to GeoTools
 Don’t worry, old syntax still supported
FOSS4G 2017, Boston
August 14th-19th 2017
* {
...
-gt-mark-label-obstacle: true;
-gt-label-priority: 200000;
-gt-label-auto-wrap: 100;
}
* {
...
mark-label-obstacle: true;
label-priority: 200000;
label-auto-wrap: 100;
}

46. GeoCSS env variable expansion
 Use @var or @var(defaultValue) in place of calling the
env function
 @var -> env(‘var’)
 @var(defaultValue)  env(‘var’, defaultValue)
 Exception for @sd
 @sd -> env(‘wms_scale_denominator’)
 to get a more fluent syntax for scale dependencies
 New in 2.12
FOSS4G 2017, Boston
August 14th-19th 2017

47. Underline and strikethrough
 New vendor options to control underline and
strikethrough
FOSS4G 2017, Boston
August 14th-19th 2017
<VendorOption name="underlineText">true</VendorOption>
<VendorOption name="strikethroughText">true</VendorOption>

48. Char and word spacing
 Control how much space there is between each
char
 And between words
FOSS4G 2017, Boston
August 14th-19th 2017
<VendorOption name="charSpacing">3</VendorOption>
<VendorOption name="wordSpacing">5</VendorOption>
charSpacing = 3 wordSpacing = 5

49. SVG marks
 Refer to a SVG file insinde
mark/WellKnownMark
 The outline of the SVG will be extracted
 Then filled and stroked as requested
 Suitable for simple shapes
FOSS4G 2017, Boston
August 14th-19th 2017
:mark {
fill: red;
stroke: yellow;
stroke-width: 3;
stroke-opacity: 50%;
}

50. More QGIS SLD export work
 In QGIS 3.0 support for label exports (thanks for
OpenGeoGroep sponsoring)
 Want to see more? Help us fund the effort 
FOSS4G 2017, Boston
August 14th-19th 2017

51. That’s all folks!
Questions?
info@geo-solutions.it
FOSS4G 2017, Boston
August 14th-19th 2017