Pragmatic Destination Descriptions 1 Running head: PRAGMATIC DESTINATION DESCRIPTIONS Pragmatic Construction of Destination Descriptions for Urban Environments

Destination descriptions are route descriptions focusing on the ‘where’ of the destination instead of the ‘how’ to reach it. They provide first a coarse reference to the destination, and then increasingly more detailed ones as the description proceeds. We introduce a definition of destination descriptions, along with an analysis of the construction and interpretation of destination descriptions grounded in pragmatic communication theory. We present a formal model enabling the selection of references for destination descriptions from models of experiential hierarchies of urban environments. This model generates route directions for people with some knowledge of the environment. Destination descriptions are usually shorter and we conjecture that the cognitive workload required during their use is lower than for equivalent turnbased directions. Pragmatic Destination Descriptions 3 Pragmatic Construction of Destination Descriptions for Urban Environments The ways people convey place descriptions, as answers to where questions, are well investigated (see, e.g., Paraboni et al., 2007; Tversky, 2003). If the situational context allows some shared knowledge about the structure of the environment to be assumed, place descriptions typically have a hierarchical structure, referring to well-known and unambiguous elements: “Where are the keys? ” “They are in the living room, on the table.” Tversky (2003) calls these elements landmarks. The same structure can be found in some route directions. Consider, for example, a passenger instructing a taxi driver in the city of Hannover, Germany: “To Luisenstrasse, please.” “? ? ” “It is in the city center, next to the opera house, off Rathenaustrasse.” This description is accepted by the taxi driver; he starts driving, finding the way on his own. In fact, the description is a place description: it describes the destination of the trip by the same strategy as in the previous example. We will call this form of route directions destination descriptions. Note that destination descriptions do not give any information about how to find the destination, as the turn-by-turn directions of classical navigation services would do. Such classical services expect no existing environmental knowledge of the user at all, only relying on their procedural knowledge, and provide, in the sense of the classical communication theory (Shannon and Weaver, 1949), complete information. Turn-by-turn directions, however, are not adequate in the situation above. On one hand, the taxi driver would be overloaded with Pragmatic Destination Descriptions 4 information that is excessive to his survey knowledge of the city. On the other hand, the passenger might not know the route but only the location of the destination. Thus, destination descriptions are a promising way to convey route directions to people with some familiarity with an environment. Destination descriptions apply for the everyday navigation of people in their home urban environment, providing the freedom of choice of the actual route to the wayfinder. They apply in cases such as finding a shop or a friend’s place in an area of the city you are not so familiar with. Since these situations occur more frequently than traveling in a completely new environment, we even estimate the need for destination descriptions being greater than for turn-by-turn directions. Accordingly, our goal is to select the references in destination descriptions automatically. The research presented in this paper addresses the hypothesis that the content of destination descriptions is independent of the length or complexity of the possible routes to the destination. We develop a computational model of selecting references for a destination description that takes as input the current location and the desired destination of the wayfinder. The model is grounded in relevance theory, a branch of pragmatic communication theory. To identify relevant references, the model accesses and navigates in hierarchical conceptualizations of urban environments, and we demonstrate that the number of references is always relatively short, and in fact independent of the properties of the possible routes to the destination. This paper is structured as follows: in the next section, we introduce our motivation in more detail and provide an overview of the current state of the art in route directions research. In Section 3, we define and discuss the concept of destination descriptions and the selection of relevant references for such directions. In Section 4, we link destination descriptions with hierarchical mental representations of space and introduce ways to structure data in integrated Pragmatic Destination Descriptions 5 experiential hierarchies usable for the task of automated selection of references for destination descriptions. Section 5 introduces a computational model for the selection of references for destination descriptions. The functionality of the model is then demonstrated on an example from the city of Hannover in Section 6. The paper concludes in Section 7 with a discussion of the main contributions and future research directions. Background The Where and the How in Spatial Communication Communication about space, such as direction giving, represents an important use of people’s spatial mental representations. People familiar with an environment share some spatial knowledge due to similar (direct or indirect) experience of their environment. This knowledge is then exploited in the place and route descriptions they exchange. Current research in navigation services concentrates on two broad areas in which methods of personalization are studied: route planning and route communication. The latter includes user interfaces, possibly with advanced interaction such as natural language (Dale et al., 2005), and content adaptation (Klippel, 2003; Richter, 2007a). In general, the focus is on wayfinders without previous experience with the environment. Klippel (2003) focused on conceptualizations of route direction elements. The identified route direction concepts were used by Klippel et al. (2003) and Richter (2007) in an approach to chunking of turn-based route directions based on the structural properties of a route in order to decrease the number of information items in the resulting directions. While providing an important step towards cognitively ergonomic communication of route knowledge, the level of detail of the directions thus provided is determined purely by the route structure and does not consider a-priori environmental knowledge of the wayfinder. Similarly, Dale et al. (2005) Pragmatic Destination Descriptions 6 implemented a system providing route descriptions of varying granularity in a city. Road status hierarchies, road lengths and turn structures were used to construct a hierarchy of chunks of instructions. The resulting directions were structured in a hierarchical tree-like representation for use on mobile devices. Note that the use of administrative street hierarchies may not necessarily reflect the hierarchies inherent in the spatial mental representations of the wayfinders, as administrative hierarchies are the result of other structuring principles than the preservation of cognitively plausibility. Due to at least coarse a-priori knowledge of the environment, locals may often find turnbased directions excessive and patronizing. They only need an unambiguous indication of the destination, and they plan how to get there on their own.