New Insights into Urbanization Based on Global Mapping and Analysis of Human Settlements in the Rural–Urban Continuum

The clear boundary between urban and rural areas is gradually disappearing, and urban and rural areas are two poles of a gradient with many continuous human settlements in between, which is a concept known as the rural–urban continuum. Little is known about the distribution and change trajectories of the various types in the rural–urban continuum across the globe. Therefore, using global land-cover data (FROM-GLC Plus) and global population data (Worldpop) based on the decision-making tree method, this study proposed a method and classification system for global rural–urban continuum mapping and produced the mapping results on a global scale in the Google Earth Engine platform. With the expansion of built-up areas and the increase in population, the global human settlements follow the pattern that develops from wildland to villages (isolated—sparse—dense), and then to towns (sparse—dense), and finally to urban areas (edge—center). From a regional perspective, there are some obvious differences: Africa is dominated by sparse villages; Asia has the highest proportion of densely clustered towns; the proportion of dense villages in Europe is high. Rural–urban continuum mapping and analysis provide a database and new insights into urbanization and differences between urban and rural areas around the world.

城乡之间的清晰边界正逐渐消解，城乡构成了一条梯度带的两极，其间分布着诸多连续的人类聚居区，这一概念被称为城乡连续体（rural–urban continuum）。目前全球范围内，针对城乡连续体中各类聚居区的分布与变化轨迹的研究仍较为匮乏。据此，本研究依托决策树方法，结合全球土地覆盖数据（FROM-GLC Plus）与全球人口数据（Worldpop），提出了一套用于全球城乡连续体制图的方法与分类体系，并在谷歌地球引擎（Google Earth Engine）平台上生成了全球尺度的制图结果。随着建成区扩张与人口增长，全球人类聚居区遵循如下演化路径：从荒地逐步发展为村落（孤立型—稀疏型—密集型），继而发展为城镇（稀疏型—密集型），最终演化为城市区域（边缘区—核心区）。从区域视角来看，各地存在显著差异：非洲以稀疏型村落为主；亚洲的密集型城镇占比最高；欧洲的密集型村落占比较高。城乡连续体制图与分析可为全球范围内的城市化研究及城乡差异分析提供数据库支撑与全新研究视角。