Abstract: A collection of modelling elements having distinct forms and changeably interengageable for assembly to one another. Each element includes information stores and signalling paths via which said stores are connected in an information transfer network to engaged elements. The information store contents are machine readable via an entry to the network and the way in which the elements have been assembled is detectable from the machine readable contents. The elements can represent constructional features, such as parts of a building, and the physical characteristics of a building of desired appearance represented by a particular assembly can be worked out and displayed from the way in which the representational elements have been assembled.