From the planner's point of view, a taxonomy of the urban daily activity spaces (DAS) is considered as an introductory step toward explaining the differential growth within an urban system. The cluster-analysis method of Rubin and Friedman (1967) is applied to the Belgian DAS, and yields three types. A first cluster identifies the large agglomerations including the older regional centres. The second and third clusters clearly show various aspects of regional structure. They demonstrate the taxonomic power of the method as well as providing a possible basis for planning policy.