Cartographic generalization in a digital environment: when and how to generalize

A key aspect of the mapping process cartographic generalization plays a vital role in assessing the overall utility of both computer-assisted map production systems and geographic information systems. Within the digital environment, a significant, if not the dominant, control on the graphic output is the role and effect of cartographic generalization. Unfortunately, there exists a paucity of research that addresses digital generalization in a holistic manner, looking at the interrelationships between the conditions that indicate a need for its application, the objectives or goals of the process, as well as the specific spatial and attribute transformations required to effect the changes. Given the necessary conditions for generalization in the digital domain, the display of both vector and raster data is, in part, a direct result of the application of such transformations, of their interactions between one another, and of the specific tolerances required. How then should cartographic generalization be embodied in a digital environment? This paper will address that question by presenting a logical framework of the digital generalization process which includes: a consideration of the intrinsic objectives of why we generalize; an assessment of the situations which indicate when to generalize; and an understanding of how to generalize using spatial and attribute transformations. In a recent publication, the authors examined the first of these three components. This paper focuses on the latter two areas: to examine the underlying conditions or situations when we need to generalize, and the spatial and attribute transformations that are employed to effect the changes.