The typology based on a grid with a resolution level of 1 km2 (a grid of one square kilometer) is used to identify three types of clusters: 'urban centres', 'urban clusters', and 'rural grid cells'. This identification is based on grid cells that share similar characteristics based on a combination of their population density and geographical contiguity (neighborhood).
The three types of clusters are defined as follows:
- urban centres (high density clusters): a cluster of contiguous 1 km2 grid cells (without diagonals) with a population density of at least 1 500 inhabitants per 1 km2 and collectively a minimum population of 50 000 inhabitants; the boundaries of the urban centre thus determined are then smoothed through including all grid cells adjacent to at least five cells (including diagonals) belonging to this urban centre;
- urban clusters (moderate density clusters): a cluster of contiguous 1 km2 grid cells (including diagonals) with a population density of at least 300 inhabitants 1 per km2 and collectively a minimum population of 5 000 inhabitants; cells classified as urban centres usually also belong to urban clusters;
- rural grid cells (low density grid cells): grid cells that are not identified as urban centres or as urban clusters.
The typology based on the grid of one square kilometer is being updated with the results of censuses, i.e. after obtaining new data on population density in the 1 km2 grid.
Cluster types are used as a basis for determing the degree of urbanisation (DEGURBA) and urban-rural typology, while indirectly they are used for determining functional urban areas and metropolitan typology.
