Modelling Cartographic Relations for Categorical Maps

Map generalisation seeks to maintain important map objects, patterns, and relationships, while suppressing unimportant ones. Hence, the spatial and semantic characteristics of map objects as well as the relations existing between them have to be detected, preserved and exploited for generalisation. Two main groups of relations can be differentiated: Horizontal relations exist on the same level of detail (LOD), or scale, and represent common structural properties. Vertical relations appear between homologous objects and object groups in a collection of the same map type but across different map scales. Focusing on thematic categorical maps, the paper emphasises the importance of horizontal and vertical relations in automated generalisation. Hence, a typology of horizontal and vertical relations for categorical maps is presented and links to existing generalisation operators are identified. A selection of relations is discussed and illustrated in more detail.