DataSheet2_Scaling Beyond Cities.CSV

City population size is a crucial measure when trying to understand urban life. Many socio-economic indicators scale superlinearly with city size, whilst some infrastructure indicators scale sublinearly with city size. However, the impact of size also extends beyond the city’s limits. Here, we analyse the scaling behaviour of cities beyond their boundaries by considering the emergence and growth of nearby cities. Based on an urban network from African continental cities, we construct an algorithm to create the region of influence of cities. The number of cities and the population within a region of influence are then analysed in the context of urban scaling. Our results are compared against a random permutation of the network, showing that the observed scaling power of cities to enhance the emergence and growth of cities is not the result of randomness. By altering the radius of influence of cities, we observe three regimes. Large cities tend to be surrounded by many small towns for small distances. For medium distances (above 114 km), large cities are surrounded by many other cities containing large populations. Large cities boost urban emergence and growth (even more than 190 km away), but their scaling power decays with distance.

城市人口规模是解析城市运行规律的关键度量指标。诸多社会经济指标随城市规模呈超线性标度关系，而部分基础设施指标则随城市规模呈亚线性标度关系。然而，城市规模的影响范畴并不局限于市域边界之内。本研究通过考察周边城市的产生与发展，分析市域边界之外的城市标度行为。基于非洲大陆城市构建的城市网络，我们开发了一套用于划定城市影响范围的算法。随后，我们在城市标度律的研究框架下，对城市影响范围内的城市数量与人口规模展开分析。我们将研究结果与该网络的随机置换结果进行对比，证实观测到的、城市促进周边城市产生与发展的标度效应并非随机因素所致。通过调整城市影响半径，我们观测到三类演化区间：在近距离范围内，大型城市周边往往分布着大量小型城镇；当中距离区间（114公里以上）时，大型城市周边则环绕着诸多人口规模庞大的城市；大型城市能够推动周边城市的产生与发展（影响范围甚至可覆盖190公里以外），但其标度效应随距离增加逐渐衰减。