In this chapter we introduce the concept of temporal-geographic information systems (TGIS). We first describe some nontemporal concepts of GIS, consider the issues of scale and of continuous and discrete data, and give a brief background to the basis of remote sensing measurements. Using the concept of the ‘data construct’ as a tool for understanding TGIS data structures, we explain the relationship between characteristics (extent, resolution and density) and domains (attribute, spatial and temporal) of each dataset. Finally, we discuss two emerging issues in TGIS: the assessment of spatial–temporal accuracy and uncertainty, and the use of metadata systems.