Geoscience Reference
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Figure 2.5. Combination of sources for identifying the cities as objects (source: [BRE 13])
Time follow-up
The UMZ database is updated regularly by the European Environment Agency.
Figure 2.6 shows the versions of this database in 1990, 2000 and 2006 for the urban
spots of Poznan and Leipzig. In this approach, which derives from a continuous-field
source, the object is only defined a posteriori, after being carved out according to the
category of “built-up” land use. Its geometry is determined that way. The object's
identification is a procedure in itself and requires an external database. In an “object”
oriented design, it is current practice to define the object before, and then to evaluate
its geometry and attributes over time. Here, the approach forces to build the
geometries and then to identify the cities at each date. This approach does not
necessarily guarantee the continuity of the identity. All the changes described in
Chapter 1 may be met: appearance, absorption or fusion and division or disappearance.
At this level, it is, therefore, necessary to put in place a genealogy system in order to
follow the life of the objects. In some contexts of rapid urbanization, it requires some
expertise to validate and eventually correct the filiations.
Figure 2.6. The different versions of the UMZ (source: [BRE 11b])
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