COMPUTER-ASSISTED GENERALIZATION - AN IMPORTANT SOFTWARE-TOOL IN GIS 
Bernd M. Powitz 
Institute of Cartography, Hannover University 
Germany 
ISPRS Commission IV 
The present expansion of GIS has also a grand effect on computer-assisted cartography. 
Nowadays there is a great demand for special software-tools and applications. GlS-users do 
need algorithms and computer-solutions for the main items of generalization and visualization. 
At the Institute of Cartography (IfK) at Hannover University it is a long tradition to work on 
research projects in the field of computer-assisted generalization. The main emphasis is 
put on the development of practical computer solutions. The actual repertoire of the IfK's 
generalization software called CHANGE consists of a lot of program modulis and algorithms 
for the automatic map design of large scale maps. 
At the IfK individual products for cartographic preparation of the traffic network and the 
buildings have been developed. A lot of difficult problems of cartographic generalization and 
creation of digital cartographic models (DCM) have yet been solved (eg. smothing, elimination, 
simplification, symbolization, selection, classification, exaggeration, combination etc). 
KEY WORDS: Generalization, Visualization, GIS-software 
1. INTRODUCTION 
The current boom in the field of geographical 
information systems (GIS) and the rapid 
development in graphic data processing have 
many consequences concerning computer 
cartography. Mainly for visualization and 
graphic output of spatial GlS-data suitable 
software solutions are necessary. These 
software modules are indispensable 
components in GIS as alongside of data 
aquisition, data storage and data management 
etc. varied and flexible possibilities for 
graphic presentation of spatial information 
have to be provided. This brings new chances 
and challenges for computer cartography and 
familiar science disciplines. 
Cartographic generalization is an imperative 
means in the visualization of spatial GlS-data. 
The generalization or visualization process 
can be divided in single elementary steps 
as selection, simplification, symbolization, 
displacement etc. apart from the necessary 
data preprocessing and data structuring. 
At present the automation of generalization 
for large scale applications is a subject 
of intensive research. Computer-assisted 
procedural solutions of particular genera- 
lization tasks refering to selected feature 
classes are nowadays available (e.g. generali- 
zation-software of Institute of Cartography 
(IfK) at Hannover University called CHANGE). 
The aim is to construct a modular program 
system in the frame of GIS through the link 
of indepentent software modules that also 
takes into account the interactions between 
single processes and thus is able to support 
effectively the visualization of spatial 
information and of course the graphic 
production of modern maps. 
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2. HISTORY 
For many years several research projects at 
the Institute of Cartography (IfK) at Hannover 
University have contained problems and tasks 
from the field of computer-assisted generali- 
zation (Powitz, 1990). In the seventies the 
prior endeavours of IfK research were 
definitions, theoretical basis and methodical 
analysis in cartographic generalization. 
The eighties were the decade of program 
developments and realisation of different 
computer-assisted generalization procedures. 
The current tasks and research projects 
of the nineties are the provision of efficient 
robust software-modules, the arranging 
of complex system-components as powerful 
software tools in GIS, the practical tests 
of generalization programs and above all 
the use of modern computer technologies 
as for example object-oriented or rule-based 
methods and procedures. 
3. SOFTWARE-CONCEPT AT THE IFK FOR 
COMPUTER-ASSISTED GENERALIZATION 
For a constructive graphic presentation 
of spatial GlS-data several software modules 
for modelling, generalization and visualization 
are necessary. These cartographically 
demanding components have to be integrated 
in GIS as powerful tools. Flexible graphical 
output in various scales and an efficient 
use of GIS-information are above all 
solutions in computer-assisted cartographic 
generalization. Cartographic generalization 
is absolutely necessary where for faultless 
legibility and good interpretation of graphic 
representation in smaller scales on one side 
given minimum dimensions have to be kept 
—— (m (o 0 FN edn ped m=