Tjr JT ^Display time 
TV T2 Real world time 
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Figure 2. Mapping from Real World Time to Display Time 
3.3 Combination of Traditional and Dynamic Variables 
Barend Kobben and Mustafa Yaman have carried out a 
preliminary test for evaluating the perceptual properties of a 
series of dynamic visual variables, The test results shows that 
the dynamic visual variable moment appears to be not very 
useful for cartographic animations unless in combination with 
the static visual variable colour and some other variables. 
Perhaps the most important conclusion has to be that selection, 
which is so important in making cartography a strong tool for 
communication, can not be effectively attained by using 
dynamic visual variables alone. The traditional variables in 
order to accompany dynamic variables are as follows: 
The SIZE of an area on a map may be changed to show changes 
in value, it represents the size modifications of the objects 
during a specified time interval. For example, the sizes of 
countries are made proportionally larger or smaller to depict the 
amount of oil or coal reserves. An animation can be used to 
transform the map of oil reserves into the map of coal reserves 
to show the differences in location of the reserves. 
SHAPE represents a unique character of each object, sometime 
the shape can tell much of the quality of a object. An area on a 
map can be made to change in shape. The shape (and size) of 
Greenland varies as a result of the influence of a map projection. 
An STP can be used to blend between the two shapes to 
accentuate the effect of the different projections. 
COLOUR is used to concept the calorific properties that 
objects to be represented. A color transition of sptio-temporal 
objects means from one colour to another during a specified 
time interval for a certain number of iterations. The colour 
animation can be used to highlight objects of interest on a map. 
The blinking of point symbol give a sense of stressing. 
OPACITY represents the animation visibility, in other words, 
the transparency of the objects from one degree of transparency 
to another during a specified time interval. The typical usages 
of the opacity animation are blinking to draw attention, fade-in 
to make objects progressively appear, and fade-out to make 
objects progressively disappear. 
DIRECTION represents the direction change of the objects 
from a starting angle to an ending angle during a specified time 
interval. Objects may be modified with direction change in 
terms of a position point. The direction animation is used to 
represent the symbols with the obvious arrow or direction. 
Another variable DENSITY is often used to represent the 
degree of scatter or assemble of spatio-temporal objects, density 
became larger if the objects became more collective, whereas it 
became smaller when the object scatter sparsely. 
By assigning the traditional variables with dynamic variables, 
the combination of them become flexible to visualize changing 
phenomenon and altering objects. Then a framework is needed 
to be created for this combination, which based on the dynamic 
symbol base. 
4. DYNAMIC VISUALIZATION BASED ON DYNAMIC 
SYMBOL BASE 
Above we have mentioned many aspects of dynamic symbol, 
which is used to visualize the spatio-temporal process, in this 
section, the dynamic symbol base is proposed to establish an 
strategy for the implementation of dynamic symbol. 
The strategy are proposed to define a procedure which can 
make a multi-versioned data into a dynamic visualization. First, 
the Spatio-temporal association will be used to build a historical 
relationship between different spatio-temporal data, then 
different Spatio-temporal processes are got and the mapping of 
time are derived, based on the dynamic symbol base, temporal 
symbol and non-temporal are created by the combination of 
dynamic variables and dynamic variables. Thus dynamic 
visualization can be displayed by a control over the time-series 
dynamic map through a visual interface. 
Figure 3 A Framework for Dynamic Visualization Base on 
Dynamic Symbol Base 
4.1 Spatio-temporal Association 
On the basis of the classification of spatio-temporal processed, 
adopting a series of algorithms for detecting changes between 
different data versions through geometry and thematic 
characteristics of spatio-temporal objects, different kinds of 
STP will be derived from the association. A time mapping 
algorithm will be used to get the relationship between real 
world time and display time as well. 
4.2 Utilization of Dynamic Symbol Base 
Here we propose a dynamic symbol base for the 
implementation of dynamic visualization, which provides a 
methodology rather than a concrete entity for the application. 
Apart from offering a base for the traditional mechanism for