Urban Unit
Each country has its own statistical definition of what it is advisable to regard as a city, and, on the basis of there, an urban population. In France, the urban or rural character of the communes and, by extension, the population which resides, is apprehended at it through the concept of urban Unité worked out by the National institute of the statistics and the economic studies (INSEE). The typology of the urban units thus makes it possible to distinguish the communes urban and rural, the communes included in an urban unit Will be considered urban. The urban population is thus the population residing in a urban district. The communes not raising of the category of the urban communes belong, in relief, with the category of the rural communes. In France, according to the definition that INSEE gives some, a urban unit is a commune or a whole of communes (known as urban) of which more half of the population lies in a zone agglomerated of more than 2.000 inhabitants in which no dwelling is separated from nearest of more than 200 meters.
Concept of urban unit and urban district
Communes belonging to an urban unit
Definition
A widespread belief regards as urban the communes more than cash 2000 inhabitants. The definition is actually somewhat more complex. A commune belongs to an urban unit and will thus be regarded as urban so more half of its population resides in an urban center, i.e. a built-up area continues at least cash 2000 inhabitants. Three cumulative conditions are thus necessary so that a commune is considered urban.- the communal territory must be completely or partly covered by a continuous built-up area. A built fabric is considered continuous if there does not exist cut of more than 200 m between two constructions. In this built-up area, the calculation of space between two constructions is primarily carried out starting from air photographs. Moreover, it will not be taken account of the rivers crossed by bridges, public grounds (gardens, cemeteries, stages, aerodromes…), nor of the industrial or commercial grounds (factories, car parks…). This built-up area can be completely included/understood in the territory of a commune or extend on several communes.
- In this continuous built-up area resides at least 2000 people (the agglomerated zone is thus regarded as urban). The calculation of the population is strictly that of the agglomerated zone, it does not matter that this one is or not distributed on the territory of several communes.
- At least 50% of the population of the commune must reside in this urban center, and this independently of the total population of the commune (a commune less cash than 2000 inhabitants can be urban).
Illustrated example
To illustrate the determination of the urban units, let us consider the common ones has, B, C, D, E, F, G and H. Having the calculation of the total population for each one of them, one cannot however deduce their urban character directly from it or not.It is indeed necessary for that to know if there exists on the territory of these communes of the zones agglomerated of more than 2000 inhabitants (of the urban center, therefore) and, if necessary, to locate the limits precisely of them. One will exclude in particular the continuous built-up areas from less than 2000 inhabitants, such as isolated hamlets or small boroughs, unless those are not distant of less than 200 meters of an urban center, in which case they will form part of it. This work is carried out using air photographs and of data on the pattern of the settlement.
In our example, there thus exist three urban centres, represented here out of orange. The zones agglomerated of less than 2000 inhabitants appear in red.
Replaçons these urban centres in the context of communal cutting. The hamlets and the small agglomerations of population will thus not be taken into account and will be thus comparable at the diffuse zones of habitat (white space). Only common D is not crossed by an urban center.
It is now advisable to determine precisely for each commune which is the share of the population residing in an urban center. This number is indicated by the blue figure.
The communes of which more than 50% of the population lives in an urban center will be regarded as urban. Those are mentioned in red.
Let us note in addition that common the B, which has only 750 inhabitants, is regarded as urban while common D and G, who have 2000 inhabitants on the whole or more, are regarded as rural. It should be noted finally that, in this classification in urban units, it is the commune as a whole which will be regarded as urban or rural. That does not mean, of course, that urban district does not have on its territory of even agricultural natural zones nor, conversely, that a rural district does not have some agglomerated zones: that means just that the majority of the population saw or does not live in a relatively important agglomerated zone.
Categories of urban units
Definitions
The membership or not of the common to an urban unit being known, it remains to define the various types of urban units. An urban unit can be made up of only one commune or a whole of communes. The agglomerated zone including/understanding more than 2000 inhabitants can indeed extremely well extend exclusively on the territory from only one commune or the territory from several communes. When the agglomerated zone extends on only one commune, the urban unit is then known as isolated city (or urban unit monocommunale). If several urban communes share the same agglomerated zone, they form an urban unit then multicommunale (or agglomeration multicommunale).Illustrated example
Applied to our cartographic example, that gives us an urban unit multicommunale (gathering the common ones has, B, C and E) and two isolated cities (common F and H).
The population of an urban unit is that of all the communes composing it, whether this population lives indeed in the urban center or not. The most populated commune will give its name to the urban unit. It will be noted finally that two urban units can be next to without forming only one of them, since there is no continuity between them. With regard to the units multicommunales, one will distinguish moreover two types of communes:
- communes of the center. The “center” can be made up of only one or a whole of communes. If a commune only represents with it more than 50% of the population of the urban unit, it will be alone city-center. In the contrary case, all the communes which have a population higher than half of that of the most important commune, like the latter, will be city-centers.
- communes of suburbs. All the other communes of the urban unit multicommunale which are not city-centers constitute the suburbs (taken here in a statistical direction).
It should be noted that the urban units multicommunales thus made up do not respect necessarily the departmental limits, as for example that which joins together Douai (Northern) and Lens (Pas-de-Calais), nor even the national borders, like in the case of Basle (Suisse), Saint-Louis (France) and Weil-amndts-Rhein (Germany). There exist a few urban units (all transborder) which have less than 2.000 inhabitants in their French part, the definition of INSEE allowing completely such a taking into account of the situation of the common neighbors. On the other hand, the urban units respect necessarily the communal limits, insofar as the urban or rural statute recognized with a commune applies to the commune in its entirety. To summarize, all common Frenchwoman thus belongs necessarily to the one of these four categories:
- district rural
- isolated city
- city centers
- common suburbs
Many urban units in France
With the Census of 1999, INSEE delimited 2.055 urban units in France including 60 for Overseas. The Metropolitan France counted 1.995 urban units which gather 44.200.000 inhabitants on the whole (out of 58.500.000,75,5% of the total). The urban units are redefined at the time of each census of the population. Many urban surfaces per section of population:
Principal urban units of France
Here a list of the urban units of France which exceeded 100.000 inhabitants in 1999:
Sources: INSEE