TOWARDS CARTOGRAPHIC ONTOLOGIES OR “HOW COMPUTERS LEARN
CARTOGRAPHY”
I. Iosifescu Enescu, L. Hurni
Institute of Cartography, ETH Zurich, Switzerland
iosifescu@karto.baug.ethz.ch
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.