Making Web Maps Prettier

Ian Turton, Astun Technology Ltd

August 2016

Summary

  • Introduction
  • Examples
  • Solutions

Surely all maps are pretty

  • Well some are and some aren't
  • check out #cartofail for examples

Styled Layer Descriptor (SLD)

  • it's a standard!
  • hardly anyone implements it!

Robots

SLD

<se:Rule>
  <se:Name>Scientific station</se:Name>
  <se:Description>
    <se:Title>Scientific station</se:Title>
  </se:Description>
  <ogc:Filter xmlns:ogc="http://www.opengis.net/ogc">
    <ogc:PropertyIsEqualTo>
      <ogc:PropertyName>featurecla</ogc:PropertyName>
      <ogc:Literal>Scientific station</ogc:Literal>
    </ogc:PropertyIsEqualTo>
  </ogc:Filter>
  <se:PointSymbolizer>
    <se:Graphic>
      <se:Mark>
        <se:WellKnownName>circle</se:WellKnownName>
        <se:Fill>
          <se:SvgParameter name="fill">#ffffff</se:SvgParameter>
        </se:Fill>
        <se:Stroke>
          <se:SvgParameter name="stroke">#000000</se:SvgParameter>
        </se:Stroke>
      </se:Mark>
      <se:Size>1.8</se:Size>
    </se:Graphic>
  </se:PointSymbolizer>
</se:Rule>

Cascading Style Sheets (CSS)

  • it's not a mapping standard
  • every one implements it differently
  • no compatibility
 * { 
        fill: lightgray;
          stroke: black;
            stroke-width: 2;
               
    }

    [PERSONS < 2000000]{
        fill: #4DFF4D;
    }

    [PERSONS >= 2000000] [PERSONS < 4000000]{
        fill: #FF4D4D;
    }

    [PERSONS >= 4000000]{
        fill: #4D4DFF;
    }

Writing SLD

  • By hand (not really good)
  • Using a GIS (OK but tiring)
  • By program (good if it knows what you want)

Hand Editing

  • use a TEXT editor (not Word)
  • Use the GeoServer editor (validating)

GIS Editors

  • QGIS
  • UDIG

QGis

  • Good styling tools
  • No Label export (yet?)

UDig

  • Good styling tools
  • Can edit raw XML
  • Some what unstable

Custom SLD Editors

  • Shapefile Viewer
  • SLDEditor

Shapefile Viewer

  • Applies ColorBrewer to a shapefile attribute
  • http://github.com/ianturton/ShapefileViewer

SLDEditor

  • Interactive GUI for writing SLDs
  • Developed by SciSys, planning to become OSGEO project
  • http://github.com/robward-scisys/sldeditor

Pretty Maps

Tips & tricks

  • set the background colour of the map (bgcolor=0x9fd9c9)
  • chose a "good" colour scheme
  • use interpolate instead of many filters
    <se:Fill>
        <se:SvgParameter name="fill">
        <ogc:Function name="Interpolate">
          <ogc:Mul>
            <ogc:Div>
              <ogc:PropertyName>gdp_md_est</ogc:PropertyName>
              <ogc:PropertyName>pop_est</ogc:PropertyName>
            </ogc:Div>
            <ogc:Literal>1000000</ogc:Literal>
          </ogc:Mul>
          <ogc:Literal>0</ogc:Literal>
          <ogc:Literal>#a63e75</ogc:Literal>
          <ogc:Literal>1000</ogc:Literal>
          <ogc:Literal>#eaa28a</ogc:Literal>
          <ogc:Literal>5000</ogc:Literal>
          <ogc:Literal>#f9cd90</ogc:Literal>
          <ogc:Literal>10000</ogc:Literal>
          <ogc:Literal>#c4ef6d</ogc:Literal>
          <ogc:Literal>20000</ogc:Literal>
          <ogc:Literal>#56a617</ogc:Literal>

          <ogc:Literal>color</ogc:Literal>
        </ogc:Function>
      </se:SvgParameter>
    </se:Fill>

Tips & tricks

  • if need be draw the layer twice
  • use geometry functions to get the centroid
  • use maths functions to calculate sizes
  <se:PolygonSymbolizer>
  <se:Geometry>
    <ogc:Function name="buffer">
      <ogc:Function name="Centroid">
        <ogc:PropertyName>geom</ogc:PropertyName>
      </ogc:Function>
      <ogc:Mul>
        <ogc:Literal>12.0</ogc:Literal>
        <ogc:Div>
          <ogc:Function name="pow">
            <ogc:PropertyName>pop_est</ogc:PropertyName>
            <ogc:Literal>0.5</ogc:Literal>
          </ogc:Function>
          <!--<ogc:Literal>1000000000</ogc:Literal> sqrt -->
          <ogc:Literal>31622</ogc:Literal>
        </ogc:Div>
      </ogc:Mul>
    </ogc:Function>
  </se:Geometry>

Tips & tricks

  • GeoServer can follow lines
      <sld:VendorOption name="followLine"> true</sld:VendorOption>
  • If you don't want to see the lines then don't add a LineSymbolizer!

Other Issues

Bad Choropleths

  • ColorBrewer to the rescue

  • both QGis and UDig provide access to ColorBrewer palettes

  • don't use rainbows unless you want to appear on #cartofail

Missing and Repeated Labels

  • Use the centroid
  • Use <VendorOption name="partials">

Finally

  • Think about how your map will look.
  • Think about your map will be used.

Questions?