Vii. Procedures to Estimate and Project the Population of Urban Areas and Urban Agglomerations

The estimation and projection of the urban population is based on observed changes in the proportion of the population living in urban areas. Therefore, the quality of the estimates and projections made is highly dependent on the quality of the basic information permitting the calculation of the proportion urban. Such information consists normally of complete counts of both the total population in a country and the total population living in urban areas. Censuses or population registers are the most common sources of those counts. To be accurate, the proportion urban should be based on counts of the total and the urban population that achieve similar levels of coverage and that reflect properly the division of the territory into urban and rural areas. However, because of the complexity and variety of situations in which the urbanization process has taken place, it is not always straightforward to divide the inhabited territory into urban and rural areas. Indeed, the criteria used to identify urban areas vary from country to country and may not be consistent even between different data sources within the same country. Furthermore, as the process of urbanization proceeds, the number and extension of the areal units qualifying as urban generally expand, so that keeping an urban vs. rural division of the territory constant over time would be misleading and would likely result in a major underestimation of the actual proportion urban.