ABSTRACT

Empirical evidence has been lacking to explain trade agglomerations within countries. Starting with a novel micro-database of road freight shipments between Spanish municipalities for the period 2003–07, we break down city (municipal) trade flows into the extensive and intensive margins and assess trade frictions and trade concentration relying on a unique generalized transport cost measure and three internal borders: NUTS-5 (municipal), NUTS-3 (provincial) and NUTS-2 (regional). We find a stark accumulation of trade flows up to a transport cost value of €189 (approximately 170 km) and conclude that this high density is not due to administrative borders effects but to significant changes in the trade-to-transport costs relationship. To support this hypothesis, we propose and conduct an endogenous Chow test to identify significant thresholds at which trade flows change structurally with transport costs. These breakpoints allow us to split the sample when controlling for internal borders, and to define trade market areas corresponding to specific transport costs that consistently reveal an urban hierarchy of cities. The results provide clear evidence with which to corroborate the predictions of Central Place Theory.

摘要

缺乏经验证据来解释国家内部的贸易集聚。从 2003-07 年期间西班牙城市之间公路货运的新型微型数据库开始，我们将城市（市政）贸易流分解为广泛和密集的边际，并根据独特的广义运输成本评估贸易摩擦和贸易集中度措施和三个内部边界：NUTS-5（市政）、NUTS-3（省）和 NUTS-2（地区）。我们发现贸易流量的明显积累高达 189 欧元（约 170 公里）的运输成本值，并得出结论，这种高密度不是由于行政边界效应，而是贸易与运输成本关系的重大变化。为了支持这个假设，我们建议并进行内生 Chow 测试，以确定贸易流量随运输成本发生结构性变化的重要阈值。这些断点允许我们在控制内部边界时拆分样本，并定义与特定运输成本相对应的贸易市场区域，这些区域始终揭示城市的城市等级。结果提供了明确的证据来证实中心位置理论的预测。