Neglected vertical linkage: A study on the form of the canal network in the Huainan Salt Area during the Ming and Qing dynasties using space syntax measurements

The Huainan Salt Area was the most essential salt production and trade base in ancient China. The government had strict control over the essential tax source region and left behind numerous official documents. However, when comparing with the modern surveying maps, we found that the boundaries between salt districts were unclear, which was obviously contradictory to the principle of independence between salt districts in official documents. Therefore, this study used the 1920s’ historical map of the Huainan Area to extract vector data such as the canal and road networks and the location of salt settlements, and then used space syntax to describe the transportation network morphology and settlement distribution structure to respond to the contradictions with higher precision. It was found that at a 2000 m × 2000 m raster resolution, the measurements of the canal network were well correlated (p = 0.645, r = 30,000) with the salt settlement distribution. Moreover, the canal network was closer to a network-like than a tree-like structure, and vertical linkage emerged. The “government-supervised and merchant-managed” policy implemented in the Qing dynasty played an essential role, and it caused a big difference in the understanding of the salt industry system between folks and officials.