This paper aims at complementing the craft of geographical information systems (GIS) professionals with methodology founded in the systems sciences. GeoInformatics (GeoI) is conceptualized as more problem-oriented than most current GIS methodologies, which are rather technical. Conceptual considerations relevant for GeoI are made, the most important being that a GeoInformatic System (GeoIS) is a concrete implementation of GeoI concepts. The problems of information system design in general and GIS design in particular are conceptualized. A theoretical framework, Living Systems Theory (Miller 1978), is presented as a base to modeling the concrete systems handled in GeoI Modeling is conceptualized as a continuous process between the concrete and the conceptual. Design is made on models that are subsequently implemented. Implementation is facilitated by prototyping. A ten-step formulation of the design methodology is presented.