Cities as spatial clusters
研究发现，如果人们根据贸易研究中常见的引力方程选择居住地，城市规模会遵循齐普夫定律，且大城市周边有更大的腹地和乡村人口，支持了城市作为空间集聚的观点。
This article shows that Zipf’s Law for cities can emerge as a property of a clustering process. If initially uniformly distributed people chose their location based on a specific gravity equation as found in trade studies, they will form cities that follow Zipf’s Law in expected value. This view of cities as spatial agglomerations is supported empirically by the observation that larger cities are surrounded by larger hinterland areas and larger countryside populations.