Landmarks: A Thought Experiment - Landmarks: GIScience for Intelligent Services - page 31

Fig. 2.1 Similarity of
triangles between body height
(a), shadow length (b), height
of the light source (c), and
distance from the pole (d, to
the peak of the shadow)

With respect to this reference point distances can be estimated: “Closer to the sun”
means a location where the walker has a shorter shadow (an embodied experience),
“near the sun” may have some context-dependent meaning related to shadow length,
and even quantities can be given, such as “within 10 step lengths from the pole under
the sun”.

Since in our thought experiment the height of the sun is related to human body
dimensions, and constant, the walker and her friends could develop over time
also a sense of distance from the pole by observing the angle of the sun above
the horizon, or the length of their body's shadow, instead of estimating steps
from path integration. With a constant height of the sun c and body height a,
the shadow length b is proportional to the current distance from the pole d b
by the similarity of triangles (Fig. 2.1 ) :

a
b D

c
d

Moreover, by applying projective geometry any walker can (re-)produce lateral
circles around the pole. In a salient distance from the pole (say, every 10 m) turning
orthogonally to their shadows they keep walking with keeping the sun constantly to
their right until they reach their starting point. These lines, imaginary or also drawn
by chalk, can play a role in the mental conceptualization of the space: “The coin was
above/below the lateral circle at 50 steps” may sound a bit arbitrary as an example,
but consider the decree by Pope Alexander VI that divided the world between Spain
and Portugal along a meridian of 100 leagues west of the Cape Verde Islands. This
line got a historic meaning, and had landmark character.
However, in order to relieve human memory from relying on tracked locomotion,
locations should be specified as points in space. We get there by adding only one
additional element to our experiment. Let us assume the walker, after finding the
coin, moves back straight to the pole (towards the light) and marks the direction to