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Proceedings of the Symposium on Progress in Data Processing and Analysis

avoid this problem by basing the greater part of his presentation on his own expe
rience and research. This approach might appear subjective, or even biased, but
it helps us to arrive at better founded statements.
The article begins by discussing the role of information systems in cartography.
Then the various aspects of the dialogue between a photogrammetric plotter and
an information system are presented and the prospects for automatic image
processing are analyzed. By summarizing all these new requirements and possi
bilities, one can sketch a large range of measuring tools for aerial photographs,
of which the analytical plotter represents only one of several other possibilities.
2 . The role of information systems
The introduction of information systems and the management of cartographic
information in databases may be considered as a revolution in cartography. It is
important to realize that the introduction of information systems is not limited to
the creation of digital plotting systems; an information system must be regarded
as a central system for storing and managing the information, including graphi
cal presentations. Generally, the main functions of an information system cover
the following features :
data acquisition
data management
data analysis
presentation of the information
The management of geometric data in an information system requires an appro
priate structure. One of the characteristics of an information system is that the
information is structured and in general object-orientated, and that neighbour
hood relations can be described. These relations are usually established by a
relational database. This is characteristic of a geographic information system,
distinguishing it from a simple plotting system.
For an outsider, the requirement of an object-orientated structuring of the data
may appear useful, but not necessarily compulsory. However, one has to realize
that a map sheet contains an enormous mass of data which not only has to be
stored but also edited and analyzed. A large-scale map easily contains up to
100.000 vectors, whereas much more can be obtained for smaller scale maps. If a
house or a part of a street has to be erased, it is often necessary to retrieve the
coordinates of more than 1.000 points, to change their code or to eliminate them
from the database. It is only when an object or a part of it can be addressed as a
whole that one can obtain the necessary flexibility to perform these operations in
an efficient way and that one can realize the superiority of an information system
as compared to an automated plotting system.
A typical working station of a geographic information system consists of a moni
tor and a digitizer. During data acquisition or data editing, the operator checks
its activities on the monitor. The same efficiency can be achieved by photogram
metric data acquisition, provided that the image displayed on the monitor of the
geographic information system can be injected into the oculars of the plotter, as
in the Wild System 9-AP. However, one condition for efficient work is that the
speed of the plotting activity not be affected by the feedback from the geographic
information system. Nevertheless, due to the complexity of relational databases,
it is difficult to meet this requirement.