National population distribution is defined as the share of inhabitants by types of regions in a given country. Population is unevenly distributed among regions within countries. Differences in climate and environmental conditions discourage settlement in some areas and encourage concentrated settlement around a few urban centres. This pattern is reinforced by the greater economic opportunities and wider availability of services that stem from urbanisation itself. This indicator is measured as a percentage of the national population.

Urban population by city size is determined by population density and commuting patterns; this better reflects the economic function of cities in addition to their administrative boundaries. Urban areas in OECD countries are classified as: large metropolitan areas if they have a population of 1.5 million or more; metropolitan areas if their population is between 500 000 and 1.5 million; medium-size urban areas if their population is between 200 000 and 500 000; and, small urban areas if their population is between 50 000 and 200 000. This indicator is measured as a percentage of the national population.

National area distribution is defined as the classification of the given country into urban, intermediate and rural regions. The OECD has established a regional typology to take into account geographical differences and enable meaningful comparisons between regions belonging to the same type. This addresses the main problem with economic analysis at the sub-national level, where the the unit of analysis "region" can mean very different things both within and among countries, with significant differences in area and population. The OECD have classified regions as predominantly rural, intermediate and predominantly urban on the basis of the percentage of population living in local rural units. This indicator is measured as a percentage of the national surface.