/// The KeySet of the Map.

     typedef MapConstKeySet<VectorMap> ConstKeySet;

     /// KeySet getter function.

     ConstKeySet keySet() const {

       return ConstKeySet(*this); 

     }

     /// The ConstValueSet of the Map.

     typedef MapConstValueSet<VectorMap> ConstValueSet;

     /// ConstValueSet getter function.

     ConstValueSet valueSet() const {

       return ConstValueSet(*this);

     }

     /// The ValueSet of the Map.

     typedef MapValueSet<VectorMap> ValueSet;

     /// ValueSet getter function.

     ValueSet valueSet() {

       return ValueSet(*this);

     }