Classifier

A classifier captures a group of values (either expressed explicitly or as a range) providing a title to each group.

You can consider a Classifier as a set of groups into which you can sort your data:

• ExplicitClassifier

  Definition of explicit classifier by hand:

      Set[] zones = new Set[3];
      // urban commercial or residencial
      zones[0] = new HashSet(Arrays.asList(new String[] { "Zone 1", "Zone 2", }));
      // municipal or crown parkland
      zones[1] = new HashSet(Arrays.asList(new String[] { "Zone 4", "Crown 2", }));
      // industrial
      zones[2] = new HashSet(Arrays.asList(new String[] { "Zone 3" }));
      
      Classifier landuse = new ExplicitClassifier(zones);
      landuse.setTitle(0, "urban");
      landuse.setTitle(1, "park");
      landuse.setTitle(2, "industrial");
  

• RangedClassifier

  Definition of a ranged classifier by hand:

      Comparable min[] = new Comparable[25];
      Comparable max[] = new Comparable[25];
      for (int i = 0; i < 25; i++) {
          min[i] = (char) ('A' + i);
          max[i] = (char) ('B' + i);
      }
      Classifier alphabetical = new RangedClassifier(min, max);
  

• As shown above each group can be provided with a title; these titles will be used in the generated styles:

      groups.setTitle(0, "Group A");
      groups.setTitle(1, "Group B");
  

• You can also automatically generate a Classifier from a FeatureCollection.

  The following “classifier” functions are available:

  • EqualInterval - classifier where each group represents the same sized range
  • Jenks - generate the Jenks’ Natural Breaks classification
  • Quantile - classifier with an even number of items in each group
  • StandardDeviation - generated using the standard deviation method
  • UniqueInterval - variation of EqualInterval that takes into account unique values

  Here is the code example with quantile:

      FilterFactory2 ff = CommonFactoryFinder.getFilterFactory2();
      Function classify = ff.function("Quantile", ff.property("name"), ff.literal(2));
      
      Classifier groups = (Classifier) classify.evaluate(collection);
  

  Example using EqualInterval to break down a continuous range of values (such as height):

      FilterFactory2 ff = CommonFactoryFinder.getFilterFactory2();
      Function classify = ff.function("EqualInterval", ff.property("height"), ff.literal(5));
      
      // this will create a nice smooth series of intervals suitable for presentation
      // with:
      // - sequential color palette to make each height blend smoothly into the next
      // - diverging color palettes if you want to make higher and lower areas stand out more
      Classifier height = (Classifier) classify.evaluate(collection);
  

  Example using Quantile to break up a list of items (such as zones):

      FilterFactory2 ff = CommonFactoryFinder.getFilterFactory2();
      Function classify = ff.function("Quantile", ff.property("zone"), ff.literal(2));
      
      // Zones assigned by a municipal board do not have an intrinsic numerical
      // meaning making them suitable for display using:
      // - qualitative palette where each zone would have the same visual impact
      Classifier groups = (Classifier) classify.evaluate(collection);