Imposing consistent global definitions of urban populations with gridded population density models: Irreconcilable differences at the national scale

Abstract

No common global definition exists of urban populations, resulting in a lack of shared standards across countries for equivalent comparisons. Therefore, I used global population models of Landscan, Worldpop, and Gridded Population of the World to generate a provisional classification of population density classes to define urban and rural by human population densities, which is an enduring attribute to differentiate urban lands from rural lands. I calibrated 2015 population density models to the United Nations 2015 global urban population estimate of 53.9% and then balanced among the population models to reach approximately the same population percentages for rural, exurban, suburban, and urban thresholds. Because the three population models varied in population distribution, with the greatest concentration of population densities in the Landscan model and the greatest dispersion in the Gridded Population of the World, different urban density thresholds were necessary for each population model. After calibration, Worldpop, which is available from years 2000 to 2020, closely matched global urban population estimates during those years. However, without an inconstant definition, for example across populous countries, low urban percentages were not plausible in India simultaneously with moderate urban percentages in China and high urban percentages in the United States. All three population models with adjusted thresholds agreed on a divergent reported urbanized or rural status for 32 countries, representing about 30% of the global population, and greatly reduced urban percentages for another 13 countries. Reconsideration of the urban status of these countries, and the surrounding regions, may change the narrative of urban condition trajectories, prospects, and related applications for research, planning, and management. While population models and adjustments to population density thresholds are not perfect, omitting multifaceted social, economic, political, and demographic histories, they do create a pathway for comparison of urban status across countries on an equal basis, unlike urban definitions that vary by country.