ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
impossible to be presented in the GIS. These features or their 
details must be eliminated. The progress is the opposite one to 
the selection. The left features must to be displayed as 
probably as detail depending on the purpose and scale. 
Purpose 
Any GIS is used for some thematic fields or purposes. In 
the case, some features are very important to the users 
and the others are not. For example, a GIS is used for 
transportation and then the roads, even pedestrians are 
important to be displayed in the GIS. Oppositely, Some 
trees, windows, chimney, even the roof of the buildings 
are unimportant to be display in the GIS. 
• Simplification 
In one word, we can not display very detail about the feature 
as the scale changing smaller. In the other hand, it is 
unnecessary to display so detail for certain purpose, we can 
not display very detail about the feature as the scale changing 
smaller. In the other hand, it is unnecessary to display so detail 
for certain purpose. The third, GIS itself is a scientific and 
artistic work, we must follow not only the reality but also 
inputting artistic elements when we display it using the GIS 
way. We must keep its position, shape, etc. correctly as 
possible as we can. At the same time, we try to make the work 
beautiful and easily understanding without destroying its 
essential shape. 
Scale 
When the scale changes we can not present all the 
features or their details that are necessary (scale change 
smaller) or oppositely. In the case, we have to eliminate 
some features or their detail that are not only 
unnecessary but also very important. 
• Bunching and Injoining 
Bunching the features with the same characteristic and close 
proximity each other together, Displaying as a feature that 
presents the volume, fill up the spaces among them and 
average (e.g. highest or lowest) high. 
There are two main reasons we use bunching for 
generalization: 
o The features are too small to be display as the real 
shape. We use bunching to show that there are 
features in the space and tell the reader the extent of 
the space. 
o We do not need to display these features one by one. 
• Displacement 
Detecting feature conflicts, removing the less important 
conflicting features, adjusting feature extents to satisfy the 
threshold of separation and keeping the relationship. In the 
example, the building has been removed to maintain the 
relationship between the road and the building when the read 
was exaggerated. 
• Exaggeration 
Increasing the spatial extent of a feature representation for the 
purpose of emphasis and legibility; for example, enlarging the 
high of a chimney and the size of the door of the example 
building, which are the main parts of the building. The chimney 
will be the obvious object for drivers, the traffic light is very 
important object for the transportation system. 
CONCLUSION AND FUTURE 
In the study, the basic algorithms were given assistant with 
simply examples. It is the first step for the future research, and 
also these algorithms need testing under more conditions. 
To enhance 3D GIS software solutions such that the users can 
produce multiple-scale and multiple-subject output more 
efficiently, both the semi-automation or automation digital 3D 
spatial data generalization and semi-automated and 
automated 3D GIS data capture in real time must be 
addressed. 
Urban facilities (on ground, under ground, in spatial) 
generalization capability into the 3D GIS product environment 
will be a challenging and main task in general usage. Special 
usage such as in building structure project design in 3D or 4D 
will be widely used in the future. 
What does the future of generalization for 3D GIS hold? 
• Short-term Plans 
> Improving the algorithms of 3D GIS generalization in 
more examples and conditions; 
> Suitable normalization for 3D GIS products; 
> Comprehensive library of standard 3D symbols and 
possibility to create new ones;