In order to distinguish between the urban and rural population for census analysis, the boundaries of distinct settlements need to be defined. This requires the creation of suburbs and extensions to existing cities and legal towns, as well as delineating boundaries for settlements which are not legally defined (called Census towns). From 1971 to 2006, Census towns were defined as a cluster of fifty or more occupied dwellings where, within a radius of 800 metres there was a nucleus of thirty occupied dwellings (on both sides of a road, or twenty on one side of a road), along with a clearly defined urban centre e.g. a shop, a school, a place of worship or a community centre. Census town boundaries where extended over time where there was an occupied dwelling within 200 metres of the existing boundary. To avoid the agglomeration of adjacent towns caused by the inclusion of low density one off dwellings on the approach routes to towns, the 2011 criteria were tightened, in line with UN criteria. In Census 2011 a new Census town was defined as being a cluster with a minimum of 50 occupied dwellings, with a maximum distance between any dwelling and the building closest to it of 100 metres, and where there was evidence of an urban centre (shop, school etc). The proximity criteria for extending existing 2006 Census town boundaries was also amended to include all occupied dwellings within 100 metres of an existing building. Other information based on Tailte Éireann mapping and orthogonal photography was taken into account when extending boundaries. Boundary extensions were generally made to include the land parcel on which a dwelling was built or using other physical features such as roads, paths etc. Extensions to the environs and suburbs of legal towns and cities were also constructed using the 100 metre proximity rule applied to Census towns. For census reports, urban settlements are towns with a population of 1,500 or more, while settlements with a population of less than 1,500 are classified as rural.