我们研究一种狭长型经济体系中的人口集聚现象，该体系中奇数个地点沿一线段均匀分布。对该经济体系的分岔分析阐明了围绕中心城市形成双子城市的机制。我们通过若干经典经济地理模型验证了该分析的有效性与实用性，这些模型展现出多种类型的分岔行为。借助该分析，我们考察了日本本州岛城市群人口分布的历史变迁。

We investigate population agglomeration in a long narrow economy, in which an odd number of places are evenly distributed over a line segment. The bifurcation analysis of this economy elucidates the mechanism of the emergence of twin cities around the central city. The validity and usefulness of this analysis are confirmed using several well-known economic geography models that display various kinds of bifurcation behaviors. By this analysis, we investigate the historical change in the population distribution in a chain of cities on Japan's Main Island.