Shows the usage of custom classes for a fine grained control about 
            the clustering behaviour.
        
        
            
                The vectorlayer in this example contains random data with an 
                attribute "clazz" that can take the values 1, 2, 3 and 4. The  
                features with clazz = 4 are considered more important than the 
                others.
            
            
                The radiobuttons on the right of the map control the 
                cluster strategy to be applied to the features.
            
            
                - 
                    No strategy
                    means that all features are 
                    rendered, no clustering shall be applied
                
- 
                    Simple cluster-strategy
                    applies the cluster 
                    strategy with default options to the layer. You should notice 
                    that many of the important features with clazz = 4 are getting
                    lost, since clustering happens regardless of feature attributes
                
- 
                    Attributive cluster-strategy
                    uses a 
                    customized cluster strategy. This strategy is configured to 
                    cluster features of the same clazz only. You should be able to see all 
                    red points (clazz = 4) even though the data is clustered. A 
                    cluster now contains only features of the same clazz.
                
- 
                    Rulebased cluster-strategy
                    uses another 
                    customized cluster strategy. This strategy is configured to  
                    cluster features that follow a certain rule only. In this case only  
                    features with a clazz different from 4 are considered as 
                    candidates for clustering. That means that usually you have fewer 
                    clusters on the map, yet all with clazz = 4 are easily 
                    distinguishable
                
                Hover over the features to get a short infomation about the 
                feature or cluster of features.