Spatio-temporal Generalization: the Chronograph Application

This paper describes research conducted in order to introduce traditionally static spatial concepts, like generalisation, into a temporal schema and study their aspects concerning Change over time. Temporal generalisation regards the representation of each object and its Changes over different time scales. It is within the logic of the proposed model to contain strict formalizations of the objects, their domains, their attributes and their Changes. Time scales can be defined at different granularities, according to the map application, as a part of the model. The model treats both objects and changes equivalently, classifying them as Essential or Non-Essential and creating class hierarchies for both. Expanding the notion of cartographic information abstraction, we term Temporal Information Abstraction as the process of transferring a spatio-temporal schema into a new schema of different spatial and temporal detail. Therefore, the four basic operators of conceptual map generalisation are utilised, thus defining four new temporal information abstraction operators: temporal selection, temporal class generalisation, change aggregation and temporal topology association. To check the operators’ efficiency and the proposed model’s suitability, an application has been developed. Its purpose is to facilitate the study of temporal generalisation, by accessing the modelled spatio-temporal schema and producing a generalised version of its objects and Changes. The four operators are applied, according to specific user needs. The final result is visualised through a variation of methods and a fidelity ratio is calculated to express the soundness of the temporally generalised schema.