Cities are complex objects and can be approached through different definitions and delineations. Several urban databases are thus currently available at European scale. As illustrated in the Figure 2.1, there is not one but at least 5 delineations of a city, according to European databases. These cities are defined either as urban agglomerations (based on continuous built-up areas, like Urban Morphological zones from EEA or Morphological Urban Areas from IGEAT) or as functional urban areas (based on commuting patterns around urban cores, like Functional Urban areas from IGEAT or Larger Urban Zones from OECD and European commission).
This diversity of delineations is not a problem in itself, since it highlights different approaches of urban facts, which can be relevant for different proposes. But it can also be a source of confusion: in the case of Wien, for instance, the comparison of the results obtained from those databases reveals very important differences, up to 25% as regards to the population of Wien functional area (2,1 millions inhabitants for LUZ_2004 2,5 for LUZ harmonized and)2,8 for FUA_IGEAT). That is why it is very important to understand the way these bases have been constructed (construction rules, sources, etc) and to elaborate a common approach, in order to compare the databases from both conceptual and technical points.
The following sections give the main keys to help the ESPON users choosing the most appropriate DB regarding their scientific targets. Four main databases were selected to be integrated into the ESPON database, in order to provide reliable and comparative information about cities as shown in Figure 2.3. This selection depends on the quality of the metadata and on the consistency of urban delineations. In particular, we have excluded the databases elaborated through a bottom-up approach as seen in Figure 2.2, for which definitions, sources and process may vary between countries (like LUZ from Urban audit 2004) and we have given priority to top-down approaches that rely on homogeneous specifications on the whole area.