Classifying urban areas by population density is fine, but what about industrial areas, don`t they count as urban areas? In addition, the built-up area per capita is closely linked to a country`s income and will distort the share of the population in cities and rural areas. To show this, we defined cities as cells of 250 by 250 meters that are built at least 50%, and rural areas as cells built at less than 25%. These thresholds are used in several built-up area definitions for urban and rural areas. The application of the degree of urbanization to the GHS-POP global population network results in an estimated share of the rural population in 2015 at 24%, which is significantly lower than the 46% based on national definitions (Figure 4). The main reason for this difference is that 12 large countries classify cities as rural areas. China and India account for half of the difference in the rural population. China`s definition makes it clear that cities and small towns are not considered urban because they use a threshold of 100,000 inhabitants for urban areas. India uses a threshold of 5,000 inhabitants but combines it with other criteria, so most cities are classified as rural. 10 other countries account for 30% of this difference: Bangladesh, Democratic Republic of Congo, Egypt, Ethiopia, Indonesia, Nigeria, Pakistan, Sudan, Uganda and Vietnam.
In short, 12 countries account for three-quarters of the difference in rural population shares. Thirty-seven countries have a national definition of urban area that includes a maximum share of employment in agriculture. These countries are mainly located in Africa and Asia. However, the share of employment in agriculture varies considerably from country to country and according to level of development. In high-income countries, it is 3 percent compared to 63 percent in low-income countries (Chart 5). The inclusion of such a criterion in a comprehensive definition would lead to entire countries becoming rural or urban, which would constitute a barrier to comparison. In addition, this share is rapidly decreasing. In 2000, agriculture accounted for 40 per cent of world employment.
By 2018, it had fallen to 28%. Therefore, the inclusion of this criterion would also reduce comparability over time. Some scientists have argued for the use of relative thresholds to define urban and rural areas. This could mean, for example, identifying the 10 most urbanized areas of a country. However, a comprehensive definition should ensure a high degree of spatial and temporal comparability. Comparing the 10 most urbanized areas of one country with the 10 most urbanized areas of another country does not guarantee that these areas have the same degree of urbanization. The degree of urbanization in the world is increasing, but a relative threshold cannot account for it either. As a result, relative thresholds do not allow for good comparability across space and time. Thank you very much for the very informative blog and the exciting arguments. I found the proposed methodology simple and attractive, but in order for it to be accepted more widely, I believe that we also need to ensure its relevance from the point of view of national decision-makers.
In Egypt, for example, according to the proposed methodology, most desert settlements declared as cities are reclassified into villages. It would be correct if we neglected the role that these settlements play in relation to the surrounding settlements, which depend on them for the provision of essential urban services – such as secondary schools or general or specialist hospitals. The inclusion of a criterion that takes into account the “urban area” may be relevant. Institutions could be called cities or municipalities if they are the only urban service providers to their neighbouring municipalities within a 15 or 30 km radius, even if they are not eligible for the proposed population and density measures. I welcome this new approach with great interest. In fact, its simplicity is its strength. Population and density are concepts that can be understood and used worldwide. As you make clear, this increases transparency and allows for a much more effective international monitoring process. However, what we gain on one side, we lose on the other.