3.1.1. The Overall Spatial Distribution of Industrial Heritage by Period

The results of the kernel density analysis of industrial heritage in each era using GIS technology are shown in Figure 3. Tianjin's industrial heritage has different characteristics in different historical periods, but overall it also reflects certain patterns: during the early modern historical period from 1860 to 1949, there were three areas where the distribution of Tianjin's industrial heritage was focused: the Sancha River estuary area at the junction of Hebei District and Hongqiao District; the city centre area at the junction of Heping, Hedong and Hebei Districts; and the Haihe River estuary area in Binhai District. The first two of these areas are located in the centre of Tianjin. The other areas have a small amount of industrial heritage and show a clear dependence on railway lines, waterways and other transportation routes for construction. During the modern historical period from 1949 to 1978, the spatial distribution of Tianjin's industrial heritage began to show a trend of scattered development: from being concentrated in the six districts of the downtown to expanding to the periphery of the city, including Xiqing District, Jinghai District and Jizhou District; from the estuary of the Hai River in Binhai District to its north, west and south; and new clusters of industrial heritage emerged in northern Tianjin.
