1. Introduction

There are a number of geographies and typologies used for international comparison of subnational statistics. These have been developed over time through consultation with organisations such as Eurostat, the Organisation for Economic Co-operation and Development (OECD), and the United Nations (UN).

As of 1 January 2021, the internationally comparable regional geography for the UK is the International Territorial Levels (ITLs) geography. This has replaced the Nomenclature of territorial units for statistics (NUTS) geographies for the UK that were operational when the UK was a member of the European Union. The International Territorial Levels and associated lookups are available to download from the Open Geography portal.

This document provides information on the various geographies and typologies utilised by various organisations for international statistical comparisons. They are split into two sections:

  1. territorial levels and typologies which are directly derived from these territorial levels

  2. the degree of urbanisation classification, including functional urban areas and their derived typologies

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2. Territorial levels

UK International Territorial Levels

Following the UK leaving the EU and the European Statistical System, the ONS has developed a domestic statistical classification framework for the UK: International Territorial Levels (ITLs). This geographic system allows continued alignment with international standards in line with the Government Statistical Service's international strategy.

The ITLs have been established initially as a mirror to the pre-existing NUTS system and are expected to follow a similar timetable to the review of the NUTS system, meaning ITLs will be reviewed roughly every three years. The next review was scheduled to be in 2024.

The upcoming ITL update has been delayed to allow further time for consideration of potential boundary changes.  For example, there are proposed changes to the ITL2 and ITL3 boundaries for Scotland that would ensure that they align with administrative boundaries, bringing them more closely in line with the methodology used in the rest of the UK. The Scottish Government are undertaking consultation on the proposed changes to the Scottish ITL and the results from this will feed into the update process.  It is anticipated that the new set of ITL boundaries will be delivered later in 2024 for adoption from Jan 2025.

New official GSS codes have been developed for the ITL geography aligned with existing NUTS codes. Statistical users are encouraged to adopt the ITL geography from 1 January 2021 as a replacement to NUTS. Lookups between NUTS and ITL geographies will be maintained and published until 2023. ITL levels, as well as NUTS, have the following set maximum and minimum populations and relationship to administrative areas:

As per the Statistics and Registration Service Act 2007 the UK Statistics Authority, advised by the National Statistician, has responsibility for developing and maintaining definitions, methodologies, classifications and standards for official statistics. On behalf of the National Statistician the ONS will collate expert advice in regard to these classifications, on a GSS-wide basis, through the Regional and Geography Committee which includes statisticians from each devolved administration.

Local administrative units (LAUs)

Within ITL 3 areas there are smaller "local administrative units" (LAUs) known as LAU 1. These are updated to the same timetable as ITLs and as such represent a "snapshot", rather than a real-time reflection of UK local authority boundaries. The LAU 1 areas act as a building block to ITL and NUTS geographies and also to the functional urban areas and OECD metropolitan areas typologies (see next section). Note, a second level, LAU 2, was withdrawn from operation in 2017 and is no longer used.

Population data for the LAU geography are available on the ONS NOMIS website. In England and Wales, LAU 1s are based on local authority districts, in Scotland they are based on Council Areas and in Northern Ireland they are whole Local Government Districts. There may not be complete alignment, however, as the update of the ITL geography every three years can result in a time lag. Similarly, there may be policy or cultural reasons for an LAU 1 to align with a particular ITL area. This can result in local authorities that do not sit perfectly within ITL 3 areas. In the UK we see this in Scotland, where the LAU 1s nest within the ITL 3 areas, but three Council Areas are split across ITL 3 areas: Argyll and Bute, Highland, and North Ayrshire.

EU NUTS framework

When the UK was a member of the European Union, it was subject to the NUTS regulation (Regulation (EC) No 1059/2003). The NUTS regulation underpins major regional development funding by the EU and provides a statistical framework for the production of harmonised European subnational statistics for EU members. The Office for National Statistics was responsible for maintaining the NUTS framework on behalf of the UK.

The NUTS classification is defined only for the member states of the EU. The UK was still a member of the EU when the underlying legal act defining NUTS 2021 was adopted so UK regions are included in NUTS 2021. However, since the UK has now left the EU, the UK will be removed from the next NUTS framework which will come into effect in 2024 (the next review).

For practical reasons the NUTS classification generally mirrors the territorial administrative division of the EU member states. This supports the availability of data and the implementation of policy. The NUTS regulation defines minimum and maximum population thresholds for the size of the NUTS regions and are the same as used for ITLs.

OECD territorial indicators

The Organisation for Economic Co-operation and Development (OECD) is an intergovernmental economic organisation with 37 member countries, founded in 1961 to stimulate economic progress and world trade. The OECD publishes a range of statistics covering regional and metropolitan geographies.

Regions within the OECD member countries are classified into two territorial levels that reflect the administrative organisation of countries. The 394 OECD large (TL2) regions represent the first administrative tier of subnational government, that is regions. The 2,258 OECD small (TL3) regions usually correspond to administrative regions. In the UK, OECD TL2 regions align with UK International Territorial Levels (ITL) level 1 regions (and NUTS level 1 regions). TL3 regions align with ITL level 3 areas (and NUTS 3 areas). The boundaries and codes are currently the same.

Territorial typologies

There are a number of existing territorial typologies used by the EU or OECD. The following are applied at the ITL 3 (NUTS 3) level with the coastal areas typology also available at the LAU 1 level.

EU coastal areas

At NUTS 3 level, the EU identifies coastal regions as those that either have a border with a coastline, have more than half their population within 50 kilometres of the coastline, or have a strong maritime influence. At LAU level, areas are classified as coastal when they border the coastline or have at least 50% of their surface area within 10 kilometres from the coastline.

OECD Urban-Rural typology (ITL 3)

The OECD Urban-Rural territorial typology is ultimately a classification of TL 3 areas. This typology is built up based on the population grid described in the Degree of Urbanisation (DEGURBA) section and has three distinctive stages:

  1.  Areas are classed as Rural is they have a population density of less than 150 inhabitants per km2.

  2. The areas are then aggregated into TL 3 regions and classified based on the proportion of the population in rural areas:

  • "predominantly rural" if the share of the population living in rural areas is higher than 50%

  • "intermediate" if the share of the population living in rural areas is between 15% and 50%

  • "predominantly urban" if the share of the population living in rural areas is below 15%

3. Furthermore, the size of the urban centres within the TL 3 regions are taken into account to reallocate regions as "intermediate" and "predominantly urban":

  • "predominantly rural" regions are re-classified as "intermediate" regions when they contain an urban centre with greater than 200,000 inhabitants which comprises at least 25% of the TL 3 regional population

  • "intermediate" regions are re-classified as "predominantly urban" regions when they contain an urban centre with greater than 500,000 inhabitants which comprise at least 25% of the TL 3 regional population

In the UK, 124 ITL 3 areas are classified as "predominantly urban", 34 as "intermediate" and 15 as "predominantly rural".

EU Urban-Rural (NUTS 3)

The EU Urban Rural typology is based on a similar methodology to the OECD urban-rural typology. The typology is built up using the population grid methodology described in the DEGURBA section like the OECD. However, the EU identified areas as rural based on consisting of less than 300 inhabitants per km2 and fewer than 5,000 people. Similarly, a 20% rural population is used to split "predominantly urban" and "intermediate" levels. The EU splits NUTS 3 areas into three rural-urban categories by:

  • "predominately rural" if the share of the population living in rural areas is higher than 50%

  • "intermediate" if the share of the population living in rural areas is between 20% and 50%

  • "predominantly urban" if the share of the population living in rural areas is below 20%

In the UK, according to the EU Urban-Rural typology, 122 TL 3 areas are classified as "predominantly urban", 39 as "intermediate" and 18 as "predominantly rural".

EU metropolitan regions

EU metropolitan regions are NUTS 3 regions or a combination of NUTS 3 regions which represent all agglomerations of at least 250,000 inhabitants. The agglomerations are identified using the Functional Urban Area geography (see Section 3). 116 out of the 179 NUTS 3 regions of the UK are part of a metropolitan region based on this typology.

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3. Degree of Urbanisation and Functional Urban Areas

Several typologies are based on a 1 kilometre2 population grid and the associated underlying population density and proximity criteria. These typologies are the Degree of Urbanisation classification, Functional Urban Areas, OECD Metropolitan Areas and the urban-rural classification. These geographies are then defined at local authority units (LAU 1) level except for the Urban-Rural classification which is defined at NUTS3 (see previous section).

Degree of urbanisation (cities, towns and suburbs, rural areas)

The Degree of Urbanisation (DEGURBA) classification splits each area into three categories, based on population density and proximity criteria using a 1 kilometre2 (km 2) population grid. Each 1km2 grid cell is split into three classifications based on their characteristics and these are eventually combined to delineate cities, towns, suburbs are rural areas. The initial grid cells are initially categorised as being as one of the following.

Urban centre (high density cluster) 

Each 1 km2 grid cell has a population density of at least 1,500 inhabitants (per km2) and with neighbouring cells also classified as urban centres which combine to have a minimum population of 50,000 inhabitants.Note: cells that are on a diagonal from each other are not considered as neighbouring cells. Gaps in groups of urban centre areas are in-filled and borders smoothed to account for industrial and commercial areas as well as parks and urban forests.

Urban cluster (moderate density cluster)

Each 1km2 grid cell has a population density of at least 300 inhabitants per km2 cell and a minimum population of 5,000 inhabitants when grouped with neighbouring similarly classified cells. This includes cells which are only linked on a diagonal.

Rural (or mostly low density cells)

Grid cells that are not identified as either a urban centre or a urban cluster. These areas mainly have a population density less than 300 inhabitants per km2, but can have a higher number of inhabitants if they form an urban cluster with fewer than 5,000 inhabitants (see urban cluster definition).

Area types 

Once the grid cells have been classified, they are then further categorised into the following three area types:

  • cities (densely populated areas) - areas that have at least 50% of their population in urban centres

  • towns, suburbs and semi-dense areas (intermediate density areas) - areas that have fewer than 50% of their population in urban centres and a maximum of 50% of their population in rural grid cells

  • rural areas (thinly populated areas) - areas with more than 50% of their population in rural grid cells

Areas can be either an administrative area (such as district, neighbourhood or metropolitan area) or a statistical area (such as census unit or wards). Several statistics are directly produced from the degree of urbanisation classification (and are available on Eurostat). For the UK, this data is aggregations of LAU1 data. Statistics are available on health, lifelong learning, education, living conditions and welfare, labour market, tourism and digital economy and society

Functional Urban Areas

The Degree of urbanisation (DEGURBA) methodology can also be subsequently used to identify Functional Urban Areas (FUA). A FUA comprises a densely inhabited city and the surrounding commuting zone and aims to include the full economic function of a city. This definition was jointly developed and owned by the EU and the Organisation for Economic Co-operation and Development (OECD). A city is firstly identified using the DEGURBA methodology, then areas (in the UK these are local administrative areas (LAU 1s)) with at least 15% of their population commuting into the city are merged with the core city to make an area that reflects the city with its commuting zone. Small areas that are completely surrounded by areas which are commuting zone are also included. There are 46 FUAs in the UK.

OECD Metropolitan Areas

FUAs with a population of 250,000 or more are identified as Metropolitan Areas by the OECD. All 46 UK FUAs are Metropolitan Areas. Statistical indicators are regularly published for these Metropolitan Areas in the OECD Metropolitan Database.

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4. Sources for international regional statistics

United Nations (UN)

The Organisation for Economic Co-operation and Development (OECD)

The Office for National Statistics (ONS)

  • The International Territorial Levels and associated lookups are available to download from the Open Geography portal.

The European Union (EU) 

The Eurostat regions and cities summary includes links to both the EU Regional database and EU Metropolitan regions as well as the Degree of urbanisation classification, rural development, urban- rural typology and interactive maps.

Also, data published on the Eurostat website can be visualised through City Statistics Illustrated, which is an interactive tool that displays city data grouped into different statistical domains.

The European City Statistics project (formerly called Urban Audit) is a European Commission sponsored project providing reliable and comparable information on selected urban areas, described as cities. More than 900 towns and cities are covered by the European City Statistics project across the EU member states, as well as Norway, Switzerland and Turkey. The UK contributed to the project up until April 2020, providing data for 170 core cities, 19 greater cities and 46 functional urban areas. A number of analytical articles on European City Statistics data were produced by ONS. The final article was on Twinned Towns while older articles can be found on the National Archives.

Eurostat publish guidance and supporting geography files for the NUTS framework.

A number of typologies associated with regions across Europe are managed through a regulation known as "TERCET", an extension of the NUTS framework.More information on EU territorial typologies available in the Eurostat Methodological manual on territorial typologies (PDF, 44.6MB).

OECD/European Commission (2020), Cities in the World: A new Perspective on Urbanisation, OECD Urban Studies, OECD Publishing, Paris.

European Union and others (2020), Applying the Degree of Urbanisation. A Methodological manual to define cities, towns and rural areas for international comparisons.

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5. Contact us

Richard Prothero, Kelly Edwards
Office for National Statistics
Email: subnational@ons.gov.uk
Telephone: +44 1329 447825 / +44 20 7112 0196

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