Introduction:What Landmarks Are, and Why They Are Important - Landmarks: GIScience for Intelligent Services - page 8

in the environment; accordingly a landmark is standing out by some properties, or
generates an experience for an individual that contributes to the mental representa-
tion of this environment and can be recalled. The other direction refers to the degree
an object is part of common knowledge. Since every person depends on their human
senses the likelihood is high that an object's outstanding properties are perceived by
many. Thus, landmarks are suited for communication of environmental knowledge.
Sorrow and Hirtle's much cited definition [ 43 ] is of this sort, reading effectively:
“Landmarks are geographic objects of outstanding visual, cultural or structural
properties”. Their experience must structure human mental representations of space.
Even the extensional approach behind Fig. 1.3 follows the intention of this
definition. In order to illustrate the effect, consider the following experiment:
Take the six landmarks ranked in the figure and order them geographically
on a blank sheet of paper. You will find arranging them not too difficult.
What you have actually achieved is an externalization of your mental spatial
representations. The same experiment can be easily translated into the context
of your own hometown. Imagine a number of prominent objects in your
hometown, and ask your friends to arrange these objects for you spatially.
Again, they will be able to produce a sketch reflecting satisfactorily the outlay
of your hometown.
In a very similar experiment by Lynch [ 28 ] people were asked to sketch their
hometown. Comparing a large number of sketches, Lynch found commonalities
in the structure of the sketches. One common element in these sketches he called
landmarks , 6 or, in his understanding, identifiable objects which serve as external
reference points.
Our definition of landmarks is purely functional: being a landmark is a role
that objects from any category can play. It emphasizes that landmarks are mental
constructs. In alignment with Meaning 1 and 2 from above it covers for objects that
stand out in an environment such that they have made (or can make) an impression
on a person's mind. This experience is not limited to visuo-spatial properties of the
object itself, nor to current properties or to shared experiences. Counterexamples
would be “the café where we met”, “the park where we had this unforgettable
picnic” or “the intersection where I was nearly killed by a car”. It is also not limited
to human-made things, as the definition by Wikipedia above might suggest; it can
equally well be a natural object such as the Matterhorn (Fig. 1.5 ) , a widely visible
mountain in the Swiss Alps with a characteristic shape, and hence frequently used
for localization and orientation. But in their function landmarks must have certain
properties, most importantly: being recognizable in the environment.
6 We will later argue that all elements Lynch has identified can be considered as landmarks.