Last updated: 5 November 2024.
Highlights
Within city statistics, the spatial units of reference are cities and functional urban areas (FUAs). These 2 concepts are based on a harmonised methodology that was developed by the Organisation for Economic Cooperation and Development (OECD) and the European Commission (EC) that can be applied on a global scale; the methodology is based purely on population size and density (thereby overcoming administrative definitions).
According to the methodology, a city consists of 1 or more small spatial units that have at least 50% of their population in an urban centre [1]. While cities are densely populated areas, FUAs are larger territories that are highly integrated from an economic point of view. At the operational level, an FUA consists of a densely populated city plus its less densely populated commuting zone, where at least 15% of employed residents commute to work in the city.
What follows is a synthetic overview of the main steps to follow in order to identify cities and define an FUA’s boundaries. For further details, please consult the latest methodological reference [2].
This chapter forms part of Eurostat’s City statistics manual.
Definition of a city
A city consists of 1 or more small spatial units with at least 50% of their population in an urban centre. A small spatial unit can be either an administrative unit or a statistical area. Examples of administrative units include a municipality, a district, a neighbourhood or a metropolitan area. Some of these administrative units also have a political role as electoral districts or in terms of local government use. Statistical areas can be census units / enumeration areas, census blocks, census tracts, wards, super output areas, named places or small areas. Examples of small spatial units used in OECD countries include communes in France, municipalities in Italy, sigungu in South Korea and census subdivisions in Canada. The best small spatial unit for this definition is the smallest unit for which commuting data are available.
The figure below shows the process through which a city is identified by intersecting the1 km² grid-based urban centre with small spatial units.
Definition of a commuting zone
Once all cities have been defined, commuting zones can be identified using the following steps
- if 15% of employed people living in a city work in another city, these cities are treated as a single city – this step is referred to as a ‘polycentricity check’
- all small spatial units with at least 15% of their employed residents working in a particular city are identified as part of the commuting zone for that city
- enclaves, in other words, small spatial units entirely surrounded by other small spatial units that belong to a commuting zone or a city are included and exclaves or non-contiguous small spatial units are excluded (see Figure 2).
It’s possible, when there is a low level of commuting flows, for a specific city to have no commuting zone. In this case, there is a perfect correspondence between the FUA and the city. An example of the delineation of an FUA is summarised in Figure 2.
When an urban centre is much bigger than the ‘central’ administrative unit
In some cases, the urban centre may stretch far beyond the boundaries of the ‘central’ local administrative unit (LAU) (or municipality). This is often the case with large capital cities that have outgrown the small LAU that carries their name. To strictly define the city as the central LAU would create a problem of ‘under-bounding’, in other words the city would be too small relative to its urban centre and a large share of the population living in the urban centre would inhabit areas outside the city. As the methodological definition of a city states that all LAUs with at least 50% of their population in the urban centre are part of the city, the boundaries of the city are extended to include these units (in order to better capture and represent all urban centres).
Although, particularly in urbanised areas, morphological definitions typically reflect reality in terms of actual urban characteristics and human activities better than administrative definitions, the latter are often more firmly anchored in people’s minds and are more often used as reference geographies in research, urban planning and policymaking. However, misunderstandings can arise when there is uncertainty about the geographical reference area under consideration. For example, the morphological definition of the city of Paris, based on the degree of urbanisation, includes 295 municipalities with a population of around 10 million inhabitants. However, the administrative and conventional definition of the city of Paris only includes the municipality of Paris with its 20 arrondissements and a population of around 2.2 million inhabitants. In order to draw attention to this discrepancy and to make the spatial references of city statistics published by Eurostat transparent, the attribute (greater city) has been added to all city names for which the morphological definition of the city doesn’t correspond to its conventional, administrative definition.
It is important to note that in contrast to the territorial classification used for Urban Audit up until 2017, ‘greater city’ is no longer used as a spatial concept. Rather, a ‘greater city’ is an attribute that is intended to serve the purpose of better understanding geographical references in European city statistics. Eurostat has therefore modified the coding system for city statistics such that the default level of analysis is the harmonised code (‘C’) – composed of greater cities and all other cities (for which no information is available at the level of the greater city).
The coding and labelling of spatial units
Coding
The coding of spatial units reflects their spatial level and is based on the use of a letter ‘C’ or ‘F’ at the end of the code to denote a city or an FUA.
The coding of spatial units remains consistent over time. This means that if the spatial units are subject to changes, such as boundary changes or revisions in their composition, the code remains the same. If changes take place, a ‘b’ flag indicating a break in the time series should be added when transmitting data.
Labelling
In general, the label (and code) used for an FUA corresponds to that of the related city, with only the letter ‘C’ or ‘F’ at the end of the code being different to specify the spatial level of reference.
The slash ‘/’ can be used to separate multiple language versions of the same city name. For example, the Belgian capital city of ‘Bruxelles/Brussel’ is labelled in French and Flemish, while the coastal Spanish city of Alicante/Alacant is labelled in Spanish and Valencian.
Source data for tables and graphs
Notes
- ↑ An urban centre (high-density cluster) is a cluster of contiguous grid cells of 1 km² (using 4-point contiguity, in other words, excluding diagonals in a 3-by-3 grid of cells) with a population density of at least 1 500 inhabitants per km² and collectively a minimum population of 50 00 inhabitants before gap-filling; if needed, cells that are at least 50% built-up may be added.
- ↑ The European Commission, the Food and Agriculture Organization of the United Nations (FAO), the United Nations Human Settlements Programme (UN-Habitat), the International Labour Organization (ILO), the Organisation for Economic Co-operation and Development (OECD) and The World Bank (2021): Applying the Degree of Urbanisation. A methodological manual to define cities, towns and rural areas for international comparisons. 2021 edition.
Explore further
Database
- City statistics (urb), see:
- Cities and greater cities (urb_cgc)
- Functional urban areas (urb_luz)
- Perception survey results (urb_percep)