Until recently, there was no harmonised definition of a city for European and OECD countries. This undermined the comparability, and thus also the credibility, of international comparative analysis of cities. To resolve this problem, the OECD and the European Commission developed a new definition of a city and its commuting zone in 2011. This new EC-OECD definition identified more than 900 cities with an urban centre of at least 50 000 inhabitants in the EU, Switzerland, Iceland and Norway. Each city is part of its own commuting zone or a polycentric commuting zone covering multiple cities. These commuting zones are significant, especially for larger cities. The cities and commuting zones put together are called Functional Urban Areas. For several urban centres stretching far beyond the city, a 'greater city' level was created to improve international comparability.
The spatial levels used:
- Functional Urban Area (FUA) - formerly known as Larger Urban Zone (LUZ)
- Greater City (formerly kernel)
- City (formerly core city)
- Sub City Districts level 1· Sub City Districts level 2.
