M. Raubal (2000). Ontology and epistemology for agent-based wayfinding simulation. in: S. Winter (Ed.), Geographical Domain and Geographical Information Systems - EuroConference on Ontology and Epistemology for Spatial Data Standards, 22-27 September 2000, La Londe-les-Maures, France. GeoInfo Series 19, pp. 85-87, Institute for Geoinformation, TU Vienna, Austria.


Wayfinding and orientation are important parts of people's daily lives. We have to find our ways through cities, through buildings, or along streets and highways. Many times people find it difficult to perform such tasks because they are not provided with adequate "knowledge in the world." Environments lack sufficient wayfinding information or their architectures are badly designed, therefore they are too complex to facilitate wayfinding. Agent-based simulation of human wayfinding before actual construction of a built environment helps to determine where people face wayfinding difficulties, why they face them, and how wayfinding information and design have to be changed to avoid such difficulties.

Ontology and epistemology of space are basic concerns during the development of an agent-based wayfinding model. By defining the ontology for a specific wayfinding domain or environment, we describe what is in this domain in a general way. Paying attention to epistemology allows us to focus on the wayfinding agent's knowledge and beliefs. In this work we look at ontology and epistemology from the viewpoint of ecological science, a multidisciplinary advance to the study of living systems, their environments, and the reciprocity between the two. In particular, we consider the sub field of ecological psychology, which proposes to study the information transactions between living systems and their environments, especially in regard to the perceived significance of environmental situations for the planning and execution of purposeful behaviors.

Our main focus lies on wayfinding in buildings and we use wayfinding in airports as a case study. The ontology of this wayfinding environment is based on the ideas of J. J. Gibson, a proponent of ecological psychology, who investigated how people visually perceive their environment. Accordingly, we subdivide the wayfinding environment into a medium, substances, and surfaces. We move in a medium (of light, sound, odor, etc.) in which there are points of observation and lines of locomotion. The substances differ in chemical and physical composition, and are structured in a hierarchy of nested units. The medium is separated from the substances of the environment by surfaces. In our case, substances are cognizing agents, such as a passenger or an employee of the airport, and non-cognizing objects, such as a door, a sign, or a check-in counter.

The epistemological question of what the wayfinding agent can know about the environment and how it can accumulate such knowledge is modeled through affordances. Gibson described the process of perception as the extraction of invariants from the stimulus flux. Surfaces absorb or reflect light and Gibson's radical hypothesis was that the composition and layout of surfaces constitute what they afford. Affordances are therefore specific combinations of the properties of substances and surfaces taken with reference to an observer. There are many affordances in the environment but the wayfinding agent perceives only the affordances relevant for the specific wayfinding task, such as a door affords opening and moving through, or a hallway affords moving along. In an airport where all the necessary wayfinding information is on yellow signs, the wayfinding agent will only utilize the affordance of perceiving a yellow sign and will ignore signs in other colors.

Agents have to be coupled with the environment in which they perceive and act. The nature of this connection is the following: the environment provides percepts (i.e., affordances) to the agent, the agent decides upon and performs actions in (and therefore on) the environment, which in turn provides new percepts (i.e., affordances), etc. The complexity of this process is influenced by the properties of the environment.

Research in spatial ontology and epistemology is an important basis for the setup of an agent-based model for wayfinding. Perception and cognition of the agent can only be modeled in a useful way if the ontological and epistemological foundations are well established. In this work we try to connect ontology of space, epistemology of space, and spatial cognition, in order to come up with a practical agent-based simulation tool for wayfinding in buildings. Such a tool will help to design buildings that facilitate wayfinding.