Landmarks: A Thought Experiment - Landmarks: GIScience for Intelligent Services - page 36

2. Order : “Go straight and at the supermarket turn left” cannot be solved on the
assumption that this next supermarket in a particular direction is also the nearest
one. Instead a principle of order comes into play. The next supermarket is the
first encountered in a particular search. By the same ordering principle one could
equally well say: “At the second supermarket turn left”.
3. Hierarchical priming : While “at the supermarket” is ambiguous, “at the super-
market on Prime Avenue” is less likely ambiguous (depending on whether the
street name is a differentiator). This hierarchical localization [ 16 , 17 ] works recur-
sively if needed, i.e., in cases where Prime Avenue either is not unambiguous or
not prominent enough. “At the supermarket on Prime Avenue, in the Southern
sector [of the environment]” is adding in this way. There is strong evidence that
spatial mental representations are hierarchically organized.

Hierarchical priming happens also through salience hierarchies of landmarks. For
example, a hierarchical description (or thought) “I found the coin in the entrance
of the supermarket, not far from the ATM” refers to the supermarket as a global
landmark, and then specializes further by another reference to a local landmark,
an ATM. Here the hierarchical priming is required for disambiguation between
the many ATMs in an environment. This way, hierarchies help to break down
large environments into manageable regions of influence. Any object or event in
the environment can be related to landmarks in a variety of ways, qualitatively
and quantitatively. Besides of something being “near the supermarket” (distance,
defining the region of influence), its location can also be characterized as “on the
way from supermarket to home” (orientation), as “on the right when travelling
from supermarket to home” (direction), as “between the supermarket and home”
(projection), or as “in the quarter of the supermarket” (topology). Quantitative
characterizations are possible as well, such as “30 m from the supermarket”. Also
the prominence of a landmark can prime the memory for a particular street segment,
as in “I found a coin in the street where the supermarket is”.

2.2 Summary

A thought experiment has illustrated the fundamental role of landmarks for struc-
turing mental representations of an environment. In the constructive approach of
the experiment we have assumed an environment that provides salient experiences
linked to locations, and expected that these experiences form anchor points in mem-
ory, and also configurations that allow relative orientation. We have in particular
learned that landmark configurations are sufficient for spatial cognitive tasks such
as orientation and wayfinding. The existence of a global frame of reference, which
is essential in any technical system, from spatial information systems to robots, is
not essential for human spatial problem solving as long as the environment provides
configurations of landmarks allowing relative orientation. We have also learned that
experiences at particular locations form landmarks, and these experiences can also
be experiences of the structure (nodes) or dimensions (edges) of the structure of an
environment.