Geoscience Reference
In-Depth Information
line. Galton considers that the objects constructed following such an approach
correspond to a higher level of abstraction than those related to a direct “object”
approach. From the cognitive point of view, an observer can move from a plenum
view, consisting, for example, of watching from a train the spatial organization of a
landscape that is passing by to an object view where he identifies relative
localizations (for example, the tree next to the church) or concentrations (for
example, several juxtaposed silos) as illustrated in Figure 1.1. From the point of
view of the computer system, it is, however, not easy to manage such round-trips
instantaneously [PEU 02].
Figure 1.1.
Field-based and object-based approaches: two points of view on the same
observable (source: UMR5600 EVS-ISG - ENSL K. Michell). For a color version of the
figure, see www.iste.co.uk/mathian/spatiotemporal.zip
These two perspectives are considered as dual, and some phenomena can be
described according to each of these perspectives [PEU 02]. This depends on the
phenomenon, of course, and on the scale at which it is considered: a tree will
naturally be conceptualized as a discrete object and the temperature in field form. In
contrast, the choice is to be made for vegetation coverage, and a number of other
phenomena call for further discussion. As a result, Plewe [PLE 98] proposes a
categorization into four conceptual models of space: - (1) the plenum is something
that fills space, and the properties that matter can be measured at each point (for
example, temperature, the nitrogen content of the soil etc.); - (2) The
regions of the
space
delimited from the data that the author calls “
categorical coverage”
; it means,
for example, built-up areas, green spaces, water surfaces etc. - (3) The
regions of the
space delimited in a formal manner
, and not necessarily from the properties of the
space. Such is the case of countries, or even of the whole set of census tracts making
up an urban unit in official statistics definitions; - (4). The
object perspective
finally, in which the objects are thought as existing by themselves. Such is the case
of the city of London, for example, which can be apprehended without reference to
the way in which its delimitation has been established. Therefore, Plewe introduces
two intermediate models that allow nuancing the fields/object dichotomy, but
