Geoscience Reference
In-Depth Information
of the specifications of ERM and EGM and a concrete comparison of the
data themselves (ESDIN D10.5 2010). An additional point is that these
pan-European products are created from national datasets that have differ-
ent characteristics. The goal of these rules is to respect these characteristics
when they are related to independent causes as is the case of the different
hierarchical level of Administrative Units for each country. However when
these discrepancies are the result of particularities created by the subjective
nature of generalisation, they are not followed. The goal is the creation of a
good quality harmonised small scale dataset and not the recreation of the
existing EGM with its disadvantages.
During the implementation of the generalisation, it has been observed that
for some data cases, generalisation rules do not exist or are proved insuffi-
cient. In these cases additional constraints have been proposed taking into
account the data specifications, generalisation procedural knowledge and
common cartographic practice. Rules that guide generalisation describe the
selection of a subset of the original data utilising their properties. These
properties may be their descriptive characteristics (attributes), their spatial
properties or their topological relationships. These selections cannot be
made unless the data and the data schema used can support their retrieval.
Structural knowledge needed by some rules is created by the auxiliary
tools presented earlier in this paper. According to the rules generalisation
operators such as aggregation, simplification and collapse are used. The
consistency rules
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have been applied in the ESDIN framework for
Built-up areas, Administrative units and Hydrography
1.
If the number of inhabitants is greater than or equal to 50 000, medium
scale Built-up Areas (polygon) are transformed to small scale Built-up
Areas (polygon).
2.
Built-up Areas polygons that belong to the same Built-up area and the
distance between them is less than 500m are aggregated.
3.
If the number of inhabitants is smaller than 50 000, medium scale
Built-up Areas (polygon) are transformed to small scale Built-up
Areas (points). The collapse generalisation operator is performed by
using the centroids of the surfaces. If a Built-up area consists of more
that one polygon, the centroid of the larger one is used.
4.
If the number of inhabitants is greater than 1 000, medium scale Built-
up Areas (points) are transformed to small scale Built-up Areas
(points).
5.
The lowest level for the small scale in the administrative hierarchy is
the NUTS3 subdivision.
