TOWARDS CARTOGRAPHIC ONTOLOGIES OR “HOW COMPUTERS LEARN CARTOGRAPHY”
I. Iosifescu Enescu, L. Hurni
Institute of Cartography, ETH Zurich, Switzerland
The paper presents the first steps towards a formal representation of basic cartographic knowledge in computer-comprehensible form. It will show also the first prototype of a cartographic ontology which is currently being developed at the Institute of Cartography, ETH Zurich.
Ontology is, in the context of computer science, a hierarchical data structure describing important concepts, relationships and rules within a specific domain, with the ultimate purpose of enabling machine understanding. The proposed cartographic ontology is centred on the concepts of map, graphic element, visual variable and symbol. The ontology presumes that every digital map (either general reference or thematic) is composed essentially of some graphic elements (either geometric primitives or pictorial elements). The graphic elements are taken to a higher level of expression by the visual variables. As in cartographic theory, the ontology considers that the building blocks for digital mapmaking are the primary visual variables (colour, opacity, texture, orientation, arrangement, shape, size, focus) and the patterns (arrangement, texture and orientation patterns). The graphic elements and the visual variables are represented in a holistic view by symbols (topographic and thematic) that can be directly interpreted by cartographic systems and consequently ready to be used for map symbolization.
The cartographic ontology is the proposed mechanism for handling the complexity of map semiotics. For example, just thematic point symbols like named diagrams (bar charts, pie charts, ring charts …) as well as some of their properties (divergent, divided, polar, proportional …), impose a significant effort on the programmers of cartographic systems. In this respect, the main contribution to the field of cartography is the inherent abstract modelling of map semiotics and rule-based symbolization in a computer-comprehensible form which is in the same time independent of a specific cartographic system.
Based on the modelled map semiotics, selected cartographic rules will be added to the cartographic ontology in the last stage of the development. Strict rules (e.g. a polygon layer should not be drawn above a line or a point layer, different layers should not have the same colour scheme) or relaxed rules (e.g. recommended colour schemes or rules for label placement) will allow cartographic systems to improve the quality of map output.
Professional cartographers can use ontology based cartographic systems for defining and testing new cartographic symbols, rules and algorithms. By editing parts of the cartographic ontology, customized symbols and symbolization rules can be descriptively created, tested and validated with a minimal effort.