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limited, more time will be spent on the improvement of the quality of the
medium scale, the content of both scales will be harmonized and the sus-
tainability of the products will be ensured.
Many medium scale spatial databases contain a number of themes that are
encoded with polygon entities such as Administrative Units, settlements,
land use etc.The goal of this paper is to present a best practice approach for
the generalisation of polygon data from medium to small scale in a GIS
environment. Best practice is a technique or methodology that, through
experience and research, has proven to reliably lead to the desired result.
Best practices for generalisation refer to operators, methods, algorithms,
models and auxiliary structures that are offered from industry-standard
GIS software and thus can be used by NMCAs. If such best practices are
adopted by NMCAs, generalisation will be performed based on the most
efficient and effective way.
2- Approach & methods
2.1 Generalisation
Generalisation methods and processes have been improved alongside
developments in science and art of cartography and have been strongly influ-
enced by progress in computer science. The application of generalisation to
a medium scale database to produce a small scale dataset can be divided
into two sub-tasks: model generalisation and cartographic generalisation
(Sarjakoski 2007; Weibel 1997). Three different models have been pro-
posed for the overall process of generalisation (Harrie and Weibel 2007):
condition-action modelling, human interaction modelling and constraint
based modelling. Since an interactive generalisation system is inadequate
for working with national spatial data due to their volume, one of the other
two models should be considered. The automated generalisation process
can be divided into several sub-processes (McMaster and Shea 1992;
Brassel and Weibel 1988), often called generalisation operators, which are
performed by generalisation algorithms. A generalisation algorithm is a
formal mathematical construct that solves a generalisation problem by
changing an object's geometry or attribute (Bader et al. 1999).
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