UN Endorses a Uniform Measure for Urbanization

The lack of a global definition of urban and rural areas is a well-known obstacle to reliable international comparisons of urbanisation and of the situation in the urban and rural areas. Data collections, such as the World Urbanization Prospects published by the UN Population Division are based on national definitions and national administrative designations. These definitions vary widely and are difficult if not impossible to replicate in another country. The administrative designation of urban and rural areas means that they are simply selected without a definition, which makes it impossible to judge how comparable they are.

Several recent global agendas call for the collection of indicators for cities, urban, and rural areas: the 2030 Agenda for Sustainable Development (UN 2015), the New Urban Agenda (UN-Habitat 2017), and the Global Strategy to Improve Agricultural and Rural Statistics (IBRD-WB 2011). Basing these indicators on a harmonized definition would facilitate international comparisons and improve the quality of rural and urban statistics in support of national policies and investment decisions.

That is why six international organizations, the European Union, The Food and Agriculture Organization of the United Nations (FAO), the International Labour Office (ILO), the Organization for Economic Co-operation and Development (OECD), the United Nations Human Settlements Programme (UN-Habitat), and the World Bank, have worked closely together to develop a harmonized definition. In March 2020, the researchers presented the work to the UN Statistical Commission, which endorsed it. In June 18, 2020, the European Union and OECD launched the group’s report, Cities of the World, A New Perspective on Urbanisation (OECD 2020) that describes the use of and technical background of the new definition, the Degree of Urbanisation.

The Degree of Urbanisation identifies three types of settlements (known as level 1):

• Cities, which have a population of at least 50,000 inhabitants in contiguous dense grid cells (>1,500 inhabitants per km2);
• Towns and semi-dense areas, which have a population of at least 5,000 inhabitants in contiguous grid cells with a density of at least 300 inhabitants per km2; and
• Rural areas, which consist mostly of low-density grid cells.

This definition can be extended in two ways: the Degree of Urbanisation level 2 and the Functional Urban Area definition. The Degree of Urbanisation level 2 identifies smaller settlements by defining: cities, towns, suburban or peri-urban areas, villages, dispersed rural areas, and mostly uninhabited areas. The Functional Urban Area Definition creates metropolitan areas by adding a commuting zone around each city. The full detail of the Degree of Urbanisation and its two extensions can be found in section 7 of a new manual which is currently in open consultation and due for publication in November.

This new definition offers several advantages:

Simplicity and transparency. It relies on the simple combination of population size and density applied to the population grid, instead of a multitude of criteria or complex and lengthy calculations. An increasing number of countries have their own population grid. Several global population grids have been estimated and are available for free, including the Global Human Settlement Layer Population Grid (GHS-POP) and World Pop. The estimated Degree of Urbanisation for each country in the world using GHS-POP can be found here.

Driven by population size and density. Population size is used by more than half of the national definitions of urban and rural areas. The thresholds used in the Degree of Urbanisation take inspiration from these national definitions. However, it uses two thresholds instead of one. For cities, it uses 50,000 inhabitants as Japan does. For towns and semi-dense areas, it uses 5,000. Out of the 100 countries that use population size threshold, 85 use the 5,000 threshold or a lower threshold. The thresholds used in the Degree of Urbanisation were also tested to ensure that they produce a valid and robust classification and a balanced population distribution across the three classes.

It helps monitor progress on the SDGs. The SDGs include a multitude of indicators that should be collected for cities, urban, and rural areas, including access to electricity, water, the Internet, and all-weather roads. Some definitions of urban areas, however, include access to water and electricity. This makes it impossible to monitor these services in urban areas because it becomes a circular argument. All urban areas have water because by definition they can only be urban if they have access to water. For example, the definitions used by Bangladesh, Cuba, and Panama all include access to drinking water. Since the Degree of Urbanisation does not include services or infrastructure, it can monitor these services in an unbiased manner in urban and rural areas.

The Degree of Urbanisation captures agglomeration economies. Since the definition relies on the spatial concentration of the population, it captures the logic of agglomeration economies. The cost of service provision tends to increase from cities to towns and semi-dense areas and then to rural areas. As a result, access to these services tends to be highest in cities and lowest in rural areas.

Cost-effective monitoring. The Degree of Urbanisation can be used to re-aggregate existing data. For example, if a statistical office has measured local employment rates, then it can calculate employment rates by Degree of Urbanisation. Geo-coded micro-data can also be aggregated. This was done for the Gallup World Poll in 115 countries and for the Demographic and Health Survey in 41 Countries, a new report by Vernon Henderson et al.

The goal of this work is to facilitate international statistical comparisons of cities and urban and rural areas across a selection of indicators. This method is not meant to replace the definitions used by national statistical institutes and ministries, but to complement them.

Lewis Dijkstra is the Head of the Economic Analysis Sector of the Directorate-General for Regional and Urban Policy in the European Commission. He is the editor the European Commission’s Cohesion Report, which analyses economic, social and environmental issues in EU regions and cities; a visiting professor at the London School of Economics; and a Penn IUR Scholar.