ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001
53
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o force which
produces power, or movement. In GIS, it is normally used to
“imply some kind of change, movement and analysis of force“
(Chrisman, 1999).
There seem to be three types of meaning by "dynamic". One
implies that the nature of the object is dynamic, e.g.. coastal
line. In this case, the “dynamic” is associated with “fuzzy".
The other means the spatial process is dynamic, e.g. soil
erosion process. In this case, the "dynamic" is associated with
"temporal". The third is related to the dynamic spatial data
structure of GIS, such as the Voronoi diagram-based spatial
data modelling, mobile spatial data modelling.
Spatial objects in the real world can, according the speed of
change, be categorized into the following three classes (see
Zhang and Hunter, 2000):
• those that are static;
• those that change slowly (and imperceptibly); and
• those that are dynamic.
Zhang and Hunter (2000) reasoned: "Objects in the first
category do not change measurably over the lifespan of the
feature being observed, for example, geological structures and
major landforms. In the second category, objects vary slowly,
for instance, vegetation cover and sea-level changes. While
they cannot be considered static, movement is not normally an
essential element of these phenomena. The objects in the
third category represent dynamic situations and the way in
which they vary can be further subdivided into three sub
categories
• positional change;
• size change; and
• shape change.
For change in position, the vital elements are time, velocity
and acceleration. For change in size, it is not motion but rather
growth and shrinkage that become important, while for change
in shape it is deformation rather than motion that is of key
interest".
Another key term is the “multi-dimensional“. The first question
arising is "what's is a dimension?" In Euclidean geometry, one
is familiar with the 3-dimensional coordinate system, X, Y and
H. This system is also a mathematical basis of current GIS. In
fact, it is a commonplace that traditional GIS are dealing with
2-D geometry and associated attributes. There are also some
2.5-D solutions such as perspectives, fire frame
representation, etc. However, the volumetric 3 dimensional
GIS is still under development. In this sense volumetric 3-D
GIS is a “multi-dimensional“ GIS already.
There are also arguments on “dimension" in spatial information
science. Davis and Williams (1989) suggested to consider
attributes as the 4 th dimension and to consider time as a fifth
dimension. Li (1994) consider scale and time as another two
dimensions. Instead of 5 dimensions, he suggests a new 3-D
coordinate system with space (Z), time (T) and scale (S) as the
three axes. In GIS, spatial analysis is then performed along
these three axes (X, T and S) or on the three planes (ZT, ZS,
TS). De Cola (1997) suggests that “all data may be
considered as existing in a space of four conceptual
dimensions, each with its unique characteristics:
• space -- continuous and unbounded;
• time - continuous and bounded in one direction
(the future);
• feature - discontinuous and unbounded;
• scale - continuous and bounded in one direction
(the finest available resolution).“
One may also find that theme has also been considered as a
basic dimension in some literature. In fact, the terms
“attribute", "feature" and “theme" have similar meaning in this
sense, the word "theme" is used in this paper. To raise scale
to a level as a basic dimension is a recent event although
scale has been considered as an important issue in many
sciences (Li, 1997, 1999). It was highly advocated by Li
(1994, 1996, 1997 and 1999). Li's arguments have been
indirectly supported by many researchers (e.g. De Cola, 1997).
Indeed, Quattrochi and Goodchild (1997) in the Epilogue of
their book also re-irritated a similar view: “Scale is a
fundamental and inescapable dimension of geographic data”.
Indeed, Lee and Molenaar (2000) have made a general
statement on the context of dynamic and multi-dimensional:
“By dynamic, we imply the ability of the system
to capture the ever-changing world, and by
multi-dimensional, we mean the liberation of
spatial data from the confines of the two-
dimensional space of traditional map. When
