Introduction:What Landmarks Are, and Why They Are Important - Landmarks: GIScience for Intelligent Services - page 10

navigational tasks, helping estimate distances and directions, etc. Finally, landmarks are
concrete, visual cues, whereas anchor-points may be more abstract elements that need not
even be point-like (e.g., a river or a whole city in a cognitive map at the regional level)”
(p. 102).

In fact, our definition does not make such a distinction between anchor points and
landmarks. Instead, we argue that, in principle:

￿ any property standing out in an environment can be shared with another person,

and

￿ that any sharing of experiences is limited to (larger or smaller) groups.

For example, 'my home' is shared with a few people, and 'Eiffel Tower' is shared
with many people. But even the Eiffel Tower is not known by the universe of all
living people. Furthermore, experience can be lived and communicated. Landmarks
can be learned from text, from maps, or from conversation (e.g., somebody may
tell me: “At that intersection I was robbed”, which attaches an outstanding memory
to this object). Thus, all what is required in a communication situation is taking a
perspective. As people do adapt themselves to their communication partner in their
choice of landmarks, so must the machine. This involves a capacity for context-
aware computing [ 6 ] . Different groups (e.g., family, colleagues, people living in the
eastern suburbs, tourists) share different sets of anchor points, or can expect that
certain landmarks can be experienced by particular individuals.
Relating the notion of landmarks to embodied experience has some tradition in
research in spatial cognition. In environmental psychology, for example, Siegel and
White wrote, “landmarks are unique configurations of perceptual events (patterns).
They identify a specific geographic location” ([ 42 ] , p. 23), and similar words can
be found elsewhere (e.g., [ 8 ] ). According to their distinctive experience, landmarks
should be “the most easily recalled attributes of a region” [ 41 ] . Sadalla et al. then go
on to “explore the function of landmarks as spatial reference points, points that serve
as the basis for the spatial location of other (nonreference) points” ( ibid. ). Similarly
the definition has been supported by neuroscience, which has shown that objects
relevant for navigation and orientation do not only engage object recognition in the
brain but also areas associated with spatial memory (e.g., [ 21 , 24 ] ).
Presson and Montello use this definition as well (“objects that are relatively
better known and define the location of other points”) in their discussion of the
nature of landmarks [ 35 ] . In particular they point out that landmarks, in order to
be able to define the location of other points (objects in our terminology), must
be distinct from these other elements in spatial memory, and central to the nature
and organization of mental spatial representations. We will come back later to a
discussion that landmarks may be stronger or weaker in their distinct experience,
and that stronger ones may be used as reference points to locate weaker ones.
In this regard, only objects that are located by reference to “better known” objects
are not landmarks. Presson and Montello continue, referring to the observation of
asymmetric distance estimates between reference and non-reference points made by
Sadalla et al.: “The relation of reference to non-reference points is assumed to be
asymmetric although the notion that there are a few elements to which many others