Two-fifths of Africans reside in urban areas with populations of less than 250,000. Projections estimate that by 2050 an additional one billion people will live in urban areas, causing an acceleration of growth for these smaller urban areas. While research and development have focused on primary cities with large populations, less is known about the dynamics of urban growth in smaller, “secondary” urban areas (SUA’s). We document the spatial distribution and temporal patterns of SUA’s in eight countries across Southern Africa between 1975 and 2015. We further explore the relationships between SUA’s growth rates and climate, land use and geographic proximity to other urban areas. Our analysis integrates spatially explicit gridded population, land use, infrastructure and climate datasets. We use descriptive statistics and spatial lag and ordinary least squares regression models to quantify SUA growth rates across three periods and explore factors that are associated with the SUA growth patterns. Average SUA growth rates are 2.44% between 1975 and 1990. We show that the climate, distance and land use significantly relate to urbanization trajectories. In addition, we find that the proximity of SUA to the largest cities also significantly relates to urban growth. Our results highlight the importance of SUA’s within broader African urbanization trends. SUA are undergoing rapid population changes and are important components of economic development processes and livelihoods. Quantifying patterns of SUA urbanization is important for elevating these small but critically important urban areas into the broader context of sustainable urbanization in Africa.

中文翻译：

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南部非洲二线城市人口增长动态

五分之二的非洲人居住在人口不足 25 万的城市地区。预测估计，到 2050 年，将有 10 亿人居住在城市地区，从而导致这些较小城市地区的增长加速。虽然研究和开发的重点是人口众多的主要城市，但对较小的“二级”城市地区 (SUA) 的城市增长动态知之甚少。我们记录了 1975 年至 2015 年间南部非洲八个国家的 SUA 的空间分布和时间模式。我们进一步探讨了 SUA 的增长率与气候、土地利用以及与其他城市地区的地理邻近性之间的关系。我们的分析整合了空间明确的网格化人口、土地利用、基础设施和气候数据集。我们使用描述性统计、空间滞后和普通最小二乘回归模型来量化三个时期的 SUA 增长率，并探索与 SUA 增长模式相关的因素。1975 年至 1990 年间，平均 SUA 增长率为 2.44%。我们表明，气候、距离和土地利用与城市化轨迹显着相关。此外，我们发现 SUA 与最大城市的距离也与城市增长显着相关。我们的结果强调了 SUA 在更广泛的非洲城市化趋势中的重要性。SUA 正在经历快速的人口变化，是经济发展过程和生计的重要组成部分。