Aims: A natural terroir unit (NTU) can be defined as a unit of land that is characterized by relatively homogenous topography, climate, geological substrate and soil. The mapping of NTUs is the first stage of data acquisition in a terroir study. This study aimed to identify NTUs using a Geographic Information System and to characterize the Stellenbosch Wine of Origin District using existing digital information at the scale of a wine producing district. Methods and results: The study area is bordered by mountains, situated close to the Atlantic Ocean and bisected by the Eerste river valley, resulting in notable spatial variation of all climatic parameters. The geology is complex due to the high degree of tectonic movement and mixing of parent material. Terrain morphological units, altitude, aspect and soil type were used as primary keys/variables for the identification of NTUs. Each of the identified units was further described with respect to the extent of the expected sea breeze effect and, for certain of the soil types, the associated parent material. A total of 1389 NTUs were identified in the Stellenbosch Wine of Origin District. Conclusions: Many of the natural terroir units identified for the Stellenbosch Wine of Origin District are of a size that is not economically or practically viable. Significance and impact of the study: The natural terroir units should be grouped into larger, more manageable and thus more viable terroir units using data relating their viticultural and oenological potential. This task will be addressed in subsequent companion papers