The most common definition applied by international organizations to separate rural and urban regions is that developed by the Organisation for Economic Co-Operation and Development (OECD). The definition distinguishes two hierarchical levels of territorial unit: local and regional. At local community level the OECD defines rural areas as communities with a population density below 150 inhabitants per square kilometre. At regional level, the OECD distinguishes larger functional or administrative units by their degree of rurality, depending on what share of the region's population lives in rural communities.