3.1.2. Distribution Focus and Aggregation Area of Industrial Heritage by Period

The spatial distribution regarding the centre of gravity and standard deviation ellipse of industrial heritage for each period were obtained using mean centre analysis and deviation ellipse analysis, respectively (Figure 4). On the whole, the centre of gravity of industrial heritage distribution in the seven periods was located roughly in the centralsouthern region of Tianjin, along the main transport routes of the Haihe River, the Jingfeng Railway and the Jinpu Railway. The centre of gravity shifts sharply from one period to the next and is generally within an outer circle with a radius of 15.59 km. In the three periods between 1914 and 1978, the centre of gravity of the industrial heritage is more concentrated, with a juxtaposition along the river. From the spatial evolution of the seven periods, the centre of gravity of industrial heritage shows a general trend of change from east to west and then east again.

Based on parameters such as the angle of rotation, the length of the long axis and the length of the short axis of the standard deviation ellipse (Table 3), the spatial distribution of industrial heritage in the seven periods can be divided into two intervals. In the four periods from 1895 to 1957, the ellipse is horizontally distributed, with an ellipse rotation angle range of 62.70–99.64◦, a long axis length range of 20.56–32.29 km and a short axis length range of 4.12–21.66 km; in the remaining three periods, the ellipse is vertically distributed, with an ellipse rotation angle range of −16.67–16.38◦ (clockwise is positive), a long axis length range of 46.64–85.04 km and a short axis length range of 27.56–35.53 km. Accordingly, it can be found that when the ellipse is laid out horizontally, it is located near the Haihe River, and the ellipse has a smaller area and a higher flatness, indicating a high degree of industrial heritage concentration; when the ellipse is laid out vertically, the distribution location is not fixed, and the ellipse has a larger area and a lower flatness, indicating a low degree of industrial heritage concentration.

**Figure 3.** Distribution of kernel density by period of Tianjin's industrial heritage.

**Figure 4.** Spatial distribution centre of gravity and standard deviation ellipse of Tianjin's industrial heritage by period.


**Table 3.** Spatial distribution's centre of gravity and standard deviation ellipse parameters by period.

3.1.3. Analysis of the Causes of the Spatial and Temporal Distribution of Industrial Heritage

The spatial and temporal evolution of Tianjin's industrial heritage is closely related to the context in which it was built. The Tianjin Machine Bureau was built in 1866 (the fifth year of the Tongzhi era of the Qing Dynasty), starting the history of early modern industry in the city of Tianjin [26]. Thereafter, the "westernization group" established a series of military industries in and around Tianjin, which became the core area of the Beiyang base [26]. In the 1880s, private capital industries were established in the area of Hai Da Dao Road (now Dagu Road), making this area the birthplace of Tianjin's early national capital machine manufacturing industry [27]. From 1902, when large-scale construction began in the national concessions, to 1937, when it basically came to a halt, the nine national concessions gradually formed a layout that began on the north side of the Sancha River estuary and ran eastwards along both sides of the river; in the same year, Yuan Shikai took over Tianjin and implemented the "New Deal", focusing on the construction of the Hebei New District immediately east of the Sancha River estuary [28]. In the first and middle of the 20th century, Tianjin gradually became the industrial centre of North China and the second largest industrial city in the country. During the fall of Tianjin after 1937, Tianjin became a rear base for the Japanese invasion of China. The Japanese government, motivated by the demands of war, built up the industry in Tianjin, enabling the development of the Tianjin machinery industry [27]. After the founding of New China in 1949, the country's economic construction focused on the development of heavy industry as the main industry, and urban development was also aimed at industrial cities, while Tianjin was not classified as a category 1 heavy industry city and was a city with a large number of industrial key projects, and its industrial status declined [30]. In the 1960s and 1970s, China carried out the "Third Line Construction" to strengthen national defence. In the nationwide "great third line" construction, the inland Third Line areas became the focus of industrial construction [31], and Tianjin, which was in the first line coastal area, lost its industrial status. In the context of the "small third line" construction, the development of industry in the city's hinterland [31], Tianjin's industrial construction also showed a pattern of decentralization.

In summary, Tianjin's industrial heritage showed a spatial and temporal trend of "clustering first, then dispersal" during the period 1860–1978. From the opening of the port of Tianjin in 1860 to the "Third Line Construction" in the 1960s, Tianjin's industrial heritage gradually clustered, showing an overall pattern of distribution along the Haihe River, the Jingfeng Railway and the Jinpu Railway. Three clusters were formed in the downtown area and at the Haihe River estuary. After the "Third Line Construction", Tianjin's industrial heritage was gradually dispersed throughout the territory of Tianjin.

#### *3.2. Relationship between Industrial Heritage Distribution and Buffer Zones*

Based on the results of the above analysis, it can be seen that the distribution of industrial heritage in Tianjin is closely linked to the important early-modern transportation lines—Haihe River, Jingfeng Railway and Jinpu Railway—and therefore, the relationship between industrial heritage sites and transportation lines was further analysed. Using the buffer zone tool of ArcGIS 10.2 software, the buffer zones of each width of the Haihe River, Jingfeng Railway and Jinpu Railway were obtained, and the intersecting and overlapping areas of each width buffer zone were fused. The number of industrial heritage sites within each width was counted using the spatial linking tool. The results are shown in Figure 5: 66 industrial heritage sites (59.5% of the total) were within 0.5 km of the main trunk, 86 industrial heritage sites (77.5% of the total) were within 1 km of the main trunk and 100 sites (90.1% of the total) were within 4 km of the main trunk. This proves that the closer Tianjin's industrial heritage is to the Haihe River, the Jingfeng Railway and the Jinpu Railway, the more dense it becomes, and the spatial layout of Tianjin's early modern and modern industrial heritage has a strong dependence on the transport routes. Based on the above analysis, the concept of an urban industrial heritage corridor called "Tianjin Industrial Heritage Route" is proposed, with the Haihe River, the Jingfeng Railway and the Jinpu Railway as the backbone of the corridor, linking the industrial heritage along the route and promoting the holistic conservation of the industrial heritage of Tianjin as a whole.

**Figure 5.** (**a**) Map of the Tianjin Industrial Heritage Buffer Zone; (**b**) cumulative percentage of industrial heritage within buffer zones of different widths in Tianjin.
