This paper proposes a new technique to setup a geographical information system (GIS) using the Semantic Data Model (SDM). The proposed technique consists of the following two steps. First, a GIS is constructed by the semantic data model at the conceptual level; Second, the physical level of the GIS is planted on a commercialized database system of relational data model (RDM). A model translator from SDM to RDM is also designed in this paper. The advantages of the proposed technique are: (1) the semantic data model provides more data abstraction primitives for the conceptual structure of a GIS than are provided by the relational data model; the concept of physical data independence can be enhanced; (2) the proposed model translator provides a valuable software tool for database designer since the problem of model transformation between the SDM and the RDM is solved automatically; (3) the physical layer of GIS using relational data model will accommodate the existing fact that the current operating GIS has to be in use continually.