Since first concepts and prototypes for integrated geographic information systems (GIS) have been designed, incorporation of time has always been a matter of research, philosophical debate, and development of innovative ideas. Commercially available informationsystem packages usually do not provide support for time integration in a satisfactory way, as their design follows a cartographic 2.5D-model approach. This shortcoming is particularly problematic when designing GIS data models for geologic (map) data, which are spatially 3D, and – by definition – temporal, as geology is all about connecting time and space to physical units. Despite its time-relevance, classical GIS-based geologic data models cannot implement time and temporal information, which is usually hard-wired into relations as attribute values. Consequently, and due to this structural problem, data integrity can be at risk, time queries are not possible, and the full potential of working with geologic map data cannot be unlocked. We herein discuss basic ontologic concepts of time in geology, and incorporate these aspects in order to provide ideas and potential solutions of approaching time in GIS-integrated data models.