A conceptual model provides the best support for federating heterogeneous datastores into a unified framework and elaborating a global consistent description of all available data. It therefore plays a central role for exchange of information within the coming information society. This paper introduces a conceptual model for applications using spatio-temporal data. We discuss in particular the features which support spatial and temporal modeling. An example of conceptual design is given using a pedology application. Advantages of our approach for database design are assessed through comparison with traditional geographical information systems modeling techniques.