ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
ed thousands of years 
zation of the reality is 
digital map/GIS is still 
our goal, namely the 
I research for 3D GIS 
examples: a) Levels of 
one, b) Symbolization 
ition and simplification 
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i these theories have 
id 2D GIS. Automation 
digital map and 2D GIS 
isic theories even there 
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oduct. How to rule a 3D 
jr its data, detail and 
3, for instance, can be 
only the walls and the 
ndows, doors, even the 
better to the user and 
The research can be a 
reference as a standard to the 3D GIS products designing and 
accepting according to the purpose. 
METHODOLOGIES 
Methodologies of generalization for 3D GIS are studied from 
four aspects in this paper. 
1. Levels of Systems 
In traditional 2D maps, also digital map/GIS, we use scales to 
level the different levels of systems. We normalize the features 
(size, symbol, etc.) for each scale. 3D GIS, however, has the 
different characteristics with 2D map/GIS. In the first level 
there are four levels normally have effects on the single steps 
of the project realization and have to be heeded from the data 
capture to the modeling up to the visualization of the feature. 
The four levels are distinguished as global, area, town, 
feature. 
• Global 
The lowest step of the detail classes is used to display the 
large distribution from a large area to the whole world. In 
this case, all the elements such as cities are show as a 
symbol (symbolization of the features). Normally, the 
function of this level is used to give the index to the system. 
The feature is almost scaled down less than 1:100,000 and 
the elements of the system are made up mainly of cities and 
roads and other thematic features. 
• Area 
The second level is often to describe an area including one 
or several first or second district of a country. At this level, a 
few thematic elements are emphasized and the features in 
the cities are more generalized to leave the main streets, 
main buildings and thematic features. The features are 
scaled from 1:100,000 to 1:25.000. 
• Town 
The more frequent useful level is used in the scale among 
1:10,000 to 1:1,000. The level system is more detail to show 
the basic elements in a city, especially the buildings. Some 
basic characteristics are necessary such as geometrical 
shapes were added to the buildings that were reconstructed 
from ground plan and building height. In addition to this it is 
possible to cover the single facades with a texture. An 
additional presentation of streets facilities and objects of the 
greens are possible. 
According to the scale and the size of the features 
(buildings), three sublevels are used to display them. 
Block Model (BM): Presentation of the buildings as 
block with or without shape of roofs, texture, spacing 
between buildings and functions, mainly street 
texturing and greens. The scale is about from 1:10,000 
to 1:5,000. 
Mixed Block Model (MBM): The middle sublevel 
presents different buildings using the four kinds of 
symbols. Some of the main buildings are separated 
alone from the block. The scale is from 1:5,000 to 
1:2,000. 
• Feature 
In this most detail class the area is defined in special rang 
such as a park, a temple or a round of buildings and the 
buildings are generated with a high level of realism. 
Additionally, in comparison with Town level, more detailed 
street objects (e.g. traffic-lights) and a more detail objects of 
the greens (e.g. detail vegetation objects) are presented. 
These objects are supplied with a photo-texture. Due to 
large data quantities only a project related visualization of 
small areas in this detail class is realized. The scale area for 
these models lays between the 1:500 and 1:50. 
Besides the defined levels above, a mixture of those is 
possible, depending on the description of the task. Within a 
certain frame, a flexible design of the respective detail class is 
possible. 
2. Symbolization 
Symbolization is concerned with choosing the symbols, line 
weights, marks, colors, etc. used to present feature 
information. This component relates directly to aspects of 
production, and focuses on the manifestation of the graphic 
representation. 
GIS itself is a collection of symbols to display the multi 
dimension world. There are some kinds of conditions we use 
symbol to show the feature, such as: 
• The feature is so small that be displayed as symbol. 
• The feature is too small to be displayed as real dimension 
but it is very important for the purpose of the GIS, we use a 
symbol to show it in the GIS. 
• We want to emphasis or display feature such as gas station 
in the transportation GIS, but unnecessary to separate the 
building to around environment, for example, we do not 
need separate a restaurant from a round of buildings. 
There are 3+1 kinds of symbols using in GIS: 
• Pictographic symbol describes the enlarged outside 
volume model of the object and encoding on geographic 
and space phenomena. 
• Abstract symbol is the sketch chosen have a “natural"(or 
at least readily learned) relation to the objects and 
categories being symbolized. 
• Authentic symbol is the conceptual constrains symbol that 
operate directly upon the graphic depiction to maintain a 
natural semiotic relation between the manifest symbol and 
the visual expectations of the GIS user. 
• Collecting symbol is the collection of abstract symbol and 
authentic symbol, and that shows the special object. 
3. Refinement 
Detail Block Model (DBM): The features are • Selection and Elimination 
presented as alone as they are according to the Selecting certain features or its elements into the final 3D GIS. 
applied purpose of the GIS. The main buildings What to be selected depends on the target scale and purpose, 
(presenting as Pictographic symbol) contain additional for instance, visual clarity. The selected features will 
presentation of building facades and further single participate further generalization operations. In the phase, we 
objects. The facilities of the street are displayed normally identify which feature will be selected and which class 
completely. of one |q nc j Q f feature will be selected roughly. In another hand, 
selectively eliminating features that are insignificant or