Worldwide Delineation of Multi-Tier City-Regions

Urban centres are pivotal in shaping societies, yet a systematic global analysis of how countries are organized around multiple urban centres is lacking. We enhance understanding by delineating city-regions worldwide, classifying over 30,000 urban centres into four tiers-town, small, intermediate, and large city-based on population size and mapping their catchment areas based on travel time, differentiating between primary and secondary city-regions. Employing a 3-hour travel time cutoff, we identify 1,403 primary city-regions, increasing to 4,210 with a 1-hour cutoff, more indicative of commuting times. Our findings reveal significant interconnectedness among urban centres and with their surrounding areas, with 3.2 billion people having physical access to multiple tiers within an hour, and 4.7 billion within three hours. Notably, among people living in or closest to towns or small cities, twice as many have easier access to intermediate than to large cities, underscoring intermediate cities' crucial role in connecting surrounding populations. This systematic identification of city-regions globally, uncovers diverse organisational patterns across urban tiers, influenced by geography, level of development and infrastructure, offering a valuable spatial dataset for regional planning, economic development, and resource management.城市中心在社会发展与塑造中发挥着核心作用，但目前仍缺乏针对各国以多城市中心为核心进行空间组织的系统性全球分析。本研究通过划定全球城市区域（city-regions），以人口规模为依据将3万余个城市中心划分为城镇、小型城市、中型城市与大型城市四个层级，并基于出行时间绘制其通勤腹地（catchment areas），同时区分一级与二级城市区域，以此深化学界对该领域的认知。本研究采用3小时出行时间阈值，共识别出1403个一级城市区域；若采用更贴合实际通勤场景的1小时出行时间阈值，则一级城市区域数量将增至4210个。研究结果显示，城市中心之间及其与周边区域存在显著的空间关联性：32亿人口可在1小时内抵达多个层级的城市中心，47亿人口可在3小时内实现该通达性。值得注意的是，在居住于城镇或小型城市且紧邻此类城镇的人群中，能够便捷抵达中型城市的人数是可抵达大型城市人数的两倍，这凸显了中型城市在连接周边人口方面的关键支撑作用。本次全球范围内的城市区域系统性识别工作，揭示了受地理条件、经济发展水平与基础设施配置影响的不同层级城市的多样化空间组织模式，并可为区域规划、经济发展与资源管理提供极具价值的空间数据集。