Geoscience Reference
In-Depth Information
The generalization process was set up following a deep analysis of the
documentation and the literature; in particular it required a careful manual
study of the correspondences between the input and output data models -
each of them comprising around 200 feature classes-, and a phase of
requirements analysis and a review of all the algorithms developed so far
in the field.
With no surprise hydrography is one of the most important feature classes
to generalize. Hydrography as a theme comprises many feature classes that
describe both man-made and natural features, flowing and still waters,
with the network of flowing waters usually represented as a node-edge
graph. As one of the most prominent natural themes, hydrography is
probably the most complex, for its big number of elements and feature
classes, its extension spanning big areas of the dataset and its being in
relation with other themes (as transport networks and settlements). The
generalization of hydrography is then a complex task, which made it one
of the first topics to focus our attention to.
1.1 Input and output data models
The GeoDBR and DB25 data models for hydrography share many simi-
larities: they both distinct watercourses between man-made (canals) and
natural (rivers), and classify them on their width. All the flowing waters
are represented in a node-edge graph and the broadest of them (both canals
and rivers) are also represented as an area.
In the input model there is a 1:1 relation between edges and areas of the
broadest watercourses (the area of a broad watercourse is divided into sec-
tions, each of them containing one edge of the graph). A node is present at
each intersection between two or more edges and also at the intersection
with the edges of other graphs, noticeably those of road and railroad net-
works.
Water bodies like ponds, lakes, swamps and so on are represented in sepa-
rate feature classes and those of them connected to the hydrography net-
work contain also edges that guarantee their connection to the graph (e.g.
edges connecting the inlet and outlet of a lake). Smaller watercourses, as
creeks and ditches, are stored in two different feature classes; creeks are
part of the hydrography graph while ditches are not.
