code: private Composite getOrCreateGroup(Object parent, String name) {
  		if (groups.containsKey(name)) {
  			return groups.get(name);
  		}
  		Composite group = new Composite(name);
  		mapWidget.getVectorContext().drawGroup(parent, group);
  		groups.put(name, group);
  		return group;
  	}
docs: Used in creating the "edges", "selection" and "vertices" groups for LineStrings and LinearRings.