**1. Introduction**

In 1986, industrial monuments were added to the World Heritage List. As a testimony to the development of human civilization and cities, industrial monuments such as ancient palaces, cities and temples have become important for carrying the history of mankind and a cultural legacy of human history [1]. Judging from the trend of international heritage conservation, large-scale, cross-regional linear cultural heritage is receiving more and more attention [2]. At the end of the 20th century, the United States and Europe put forward the ideas of the "heritage corridor" and "cultural routes", which are regional scales for the conservation of industrial heritage [3,4]. In Europe, the European Route of Industrial Heritage (ERIH) was created in 1999 to support the development of industrial heritage tourism routes [5]. For the conservation of industrial heritage in China, although the National Cultural Heritage Administration has issued the *Wuxi Recommendations* on industrial heritage conservation in 2006, heralding the rise of research and conservation of industrial heritage on a national scale [6–8], in concrete conservation practice, the existing legal system and policy and institutional framework for conservation and use remain the same as when they started in 2006 [9,10], and the research and discussions are still dominated by individual cases. The reuse of industrial heritage is also focused on the factory and building level [11–13]. On the whole, policies, research and practices related to

**Citation:** Zhang, J.; Sun, H.; Xu, S.; Aoki, N. Analysis of the Spatial and Temporal Distribution and Reuse of Urban Industrial Heritage: The Case of Tianjin, China. *Land* **2022**, *11*, 2273. https://doi.org/10.3390/land11122273

Academic Editors: Lucia Della Spina, Paola Pellegrini, Antonia Russo, Maria Rosa Valluzzi and Angela Viglianisi

Received: 9 November 2022 Accepted: 7 December 2022 Published: 12 December 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

industrial heritage remain on a case-by-case basis, and there is a lack of both comprehensive analysis and the construction of conservation systems of industrial heritage at the regional level [7,8].

Recently, the application of GIS in the field of heritage conservation has been expanded to include cultural resource management [14–17], heritage monitoring and restoration [18–20] and other aspects. In addition, the research method of applying GIS technology to analyse the spatial and temporal distribution of cultural heritage is widely used [21–24]. The above GIS development directions also provide new ideas for the conservation of industrial heritage. As a geographical information platform, GIS can visualise the distribution of industrial heritage into urban territorial space and use it as a basis for a more objective analysis of the characteristics related to the spatial distribution of industrial heritage in the city using GIS tools. At the regional level, the use of GIS technology to analyse the spatial and temporal distribution characteristics and the conservation and reuse status of industrial heritage at the regional level can help to improve the comprehensive and scientific understanding of industrial heritage in a region, while providing a wider source of information and more scientific analysis results for conservation decisions in urban planning. It can also provide a reference for industrial heritage conservation in various cities. Tianjin plays an important role in China's early modern and modern history, and is known as "Tianjin witnessed one hundred years of Chinese history". [25]. In 1860, Tianjin was opened as a port and became a "nine-country concession", marking the beginning of the early modernisation process in Tianjin [26]. Since then, the construction during the Westernization Movement made Tianjin the core area of the Beiyang base [26]; the rise of private capital made the area around Haidadao Road the birthplace of national machine manufacturing [27]; the construction of the "nine-country concession" and the implementation of the New Deal at the end of the Qing Dynasty brought about an industrial boom in the Sancha River estuary area [28]; and Tianjin became a rear base for the Japanese invaders after the fall of Tianjin at the beginning of the War of Resistance Against Japan [28]. Before the founding of the People's Republic of China, Tianjin was the industrial centre of northern China, and thus left behind many outstanding industrial legacies [29]. After the founding of the People's Republic of China, Tianjin's industrial status declined and industrial construction began to develop in the hinterland in the context of the "Third Front Movement" [30,31]. The steady development of modern industry in Tianjin still left a certain amount of industrial heritage in Tianjin [32]. Tianjin's industrial heritage is characterised by its early age, important status, richness of types and distinctive spatial distribution [29]. The history of Tianjin's growth is that of the "northern economic centre" [33]. There have been some achievements in the study of Tianjin's industrial heritage as a whole, such as the identification and classification of the scientific and technological value of Tianjin's industrial heritage [34], the composition and characteristics of Tianjin's industrial heritage groups [35] and the construction of Tianjin's industrial heritage corridor system [36], but a systematic and quantitative analysis of Tianjin's industrial heritage is still lacking. The research object of this paper is the industrial heritage of Tianjin from 1860 to 1978. Using GIS technology, we analysed the spatial and temporal distribution characteristics of Tianjin's industrial heritage and the conservation and reuse status of various types of industrial heritage, so as to provide a quantitative data basis for the regional conservation of Tianjin's industrial heritage. The urban industrial heritage, as the material foundations of the city, often occupies a prime location and a large space in the city [37,38], and it is an important aspect of sustainable urban development to make efficient use of its existing derelict physical space for future use, rather than adopting a "large-scale demolition or construction" model.

#### **2. Data Sources and Research Methods**

#### *2.1. Data Sources*

The data were derived from the results of "Comprehensive Census of Industrial Heritage in Tianjin". The census was commissioned by the Tianjin Municipal Bureau of Planning (merged into Tianjin Municipal Bureau of Planning and Natural Resources in 2018), and the process and results were monitored and checked. The team collected relevant historical information to establish a list of factories and related facilities that existed historically within Tianjin. There are two sources of original material, one from the relevant archival materials in the Tianjin Municipal Archives and the National Library of China, and the other from relevant works and papers, such as: *China's Early Modern Industrial History Data* (Jingyu Wang), *The History of Modern Chinese Industry* (Cishou Zhu), *Tianjin Historical Materials* (Institute of History, Tianjin Academy of Social Sciences), *History of Railway Development in China* (Shixuan Jin and Wenshu Xu), *Tianjin Urban Planning Records* (Tianjin Urban Planning Journal Compilation Committee), *A Brief History of Urban Construction in Tianjin* (Hong Qiao) and *Inestigation on Tianjin's Modern Autonomous Industrial Heritage* (Hong Ji). Due to the lack of documentation on the state of preservation of the listed factories in recent years, more than 20 PhD and MA students were organised to conduct on-site research based on the list between 2010 and 2012, after which the research was systematically collated. The methods used for the research included: GPS geographic information acquisition, building mapping, photographic documentation, heritage overview documentation, conversation status documentation, primary source material acquisition and interviews with relevant people.

The census work used the unified "Tianjin Industrial Heritage Survey Form" (Table S1), which was divided into the "Tianjin Industrial Heritage Buildings/Structures Survey Form" and the "Tianjin Industrial Heritage Plants Survey Form", the executive summary of which is shown in Table 1. In terms of the temporal scope of industrial heritage, the development of Tianjin's modern industry was combined with studies related to China's industrial development [39,40]. The opening of Tianjin in 1860 marked the beginning of modern industry in Tianjin [26], and after the Third Plenary Session of the Eleventh Central Committee in 1978, China's industry entered a new stage of rapid development, but because it is relatively recent, the industrial heritage built after 1978 has received less academic attention, and only very little is known in the country [41]. The time frame of the industrial heritage surveyed was therefore limited to the period 1860–1978, and the definition of industrial heritage was based on The Nizhny Tagil Charter and the Taipei Declaration for Asian Industrial Heritage [42,43].


**Table 1.** Synopsis of the Tianjin Industrial Heritage Survey Form.

The Tianjin Industrial Heritage Census took two years to complete, and at the end of 2012, a total of 120 items of industrial heritage had been identified during the census. Subsequently, based on the census results, the group conducted regular follow-up surveys of Tianjin's industrial heritage, which was finally identified as 111 items as of June 2020 due to the demolition of factories caused by urban development and construction.

#### *2.2. Research Methods*

The research process of this paper was to import the data of base map elements—such as the Tianjin city area, boundaries of districts and counties, and major rivers, railways and roads; and the data of industrial heritage sites obtained from the above census in GIS format. Based on this, the analysis tools in GIS software—kernel density tool, mean centre tool, standard deviation ellipse tool and buffer zone tool—were used to generate the corresponding analysis maps (Figure 1). The kernel density analysis can visualise and abstract the overall distribution of industrial heritage in Tianjin at different periods and facilitate comparison of changes between periods. The standard deviation ellipse tool can analyse the strength of agglomeration and changes in agglomeration areas of industrial heritage at different periods. Mean centre analysis can determine the centre of gravity of industrial heritage and its movement trend at different periods. The buffer zone tool can analyse the trend of distribution of industrial heritage along major transport routes in Tianjin. In this process, GIS firstly provided a platform for overlaying the two types of data mentioned above, and secondly, the various analysis tools included in GIS helped to visualise the results more accurately and quickly, preventing the process of calculating the results from formulas and then converting them into images and providing easy conditions for the verification of such results.

**Figure 1.** Data analysis process.

#### 2.2.1. Kernel Density Analysis

Kernel density estimation. The kernel density function was used to correlate industrial heritage sites in Tianjin for probability estimation. Based on the kernel density estimation, it is possible to distinguish the spatially distributed areas of concentration of industrial heritage in Tianjin in different dimensions, such as time and type. The function is expressed as a bivariate probability density function whose value in space is centred on a known point and tends to zero over a range of widths. The Rosenblatt–Parzen kernel density estimation formula is commonly used [44].

$$R(\mathbf{x}) = \frac{1}{nh} \sum\_{i=1}^{n} k(\frac{\mathbf{x} - \mathbf{x}\_i}{h}) \tag{1}$$

In the formula, *R*(*x*) is the probability value of element *R* at *x*. In this study, *R* is the industrial heritage site. *k x*−*xi h* is the kernel function, where (*x* − *xi*) is the distance from the estimated value point *x* to the industrial heritage site *xi*; *h* is the bandwidth and is greater than 0. Studies have shown that the kernel function has a minimal effect on the results and h has a large effect, and there is no authoritative formula for determining the value of *h*. The author determined the value of *h* to be 1 km based on several experiments.

### 2.2.2. Mean Centre and Standard Deviation Ellipse Analysis

The migration of the spatial coordinates of the mean centre in different periods can characterise the trend of change in the spatial distribution of industrial heritage in Tianjin. The standard deviation ellipse can characterise the main distribution range, directional trend and degree of aggregation of industrial heritage sites in Tianjin in each period. The area of the calculated range characterizes the size of the distribution range, the direction of

the long axis reflects the directional trend of the distribution of elements and the short axis represents the distribution range [45,46]. Larger values of flatness indicate higher spatial aggregation. The formula is as follows.

$$\mathbf{C} = \frac{1}{n} \begin{pmatrix} \sum\_{i=1}^{n} \overline{\mathbf{x}}\_{i}^{2} \sum\_{i=1}^{n} \overline{\mathbf{x}}\_{i} \overline{\mathbf{y}}\_{i} \\ \sum\_{i=1}^{n} \overline{\mathbf{x}}\_{i} \overline{\mathbf{y}}\_{i} \sum\_{i=1}^{n} \overline{\mathbf{y}}\_{i}^{2} \end{pmatrix}, \begin{cases} \left(\mathbf{x}\_{i} - \overline{\mathbf{x}}'\right) \\ \left(\mathbf{y}\_{i} - \overline{\mathbf{y}}'\right) \end{cases} \tag{2}$$

In the formula, *x*, *y* are the mean centroid coordinates; *xi*, *yi* are the *i*-element coordinate values; and *n* is the total number of elements.

#### 2.2.3. Buffer-Zone Analysis

Based on the buffer-zone widths with gradients of 0–4 km, the buffer zones were calculated for water systems, railways and other transportation elements; and the buffer zones were analysed with the overlapping distribution of Tianjin's industrial heritage site elements to generate an analysis map with the percentages of the numbers of industrial heritage sites in the buffer zones of different widths of the total. Three representative buffer-zone widths of 0.5, 1 and 4 km were selected for illustration to determine whether Tianjin's industrial heritage has a correlation with the distribution of main transport routes.

#### **3. Results**

Based on the above census results, the Tianjin Industrial Heritage Census GIS Database was established (Figure 2). The database's framework mainly includes two categories, industrial-heritage elements and base-map elements in Tianjin. The industrial-heritage elements include plant-point elements, building-point elements and structure-point elements; the base map elements include Tianjin-city-boundary elements, Tianjin-districtand Tianjin-county-boundary elements, major-river elements, major-railway elements and urban-road elements. The source of the industrial-heritage elements was the results of the Tianjin Industrial Heritage Census, and the source of the base map elements was the National Basic Geographic Information System.

### *3.1. The Spatial and Temporal Distributions of Industrial Heritage*

According to previous studies, such as *China's Early Modern Industrial History Data* (Jingyu Wang et al.) and *The History of Modern Chinese Industry* (Cishou Zhu), and taking into account the history of early modern and modern industrial development in Tianjin, the stages of early modern and modern industrial development in Tianjin can be divided into seven phases, among which, the early modern period can be divided into: (1) the embryonic period of early modern industry (1860–1894), (2) the development period of early modern industry (1895–1913), (3) the prosperity of early modern industry (1914–1936) and (4) the decline of early modern industry (1937–1949). The modern period can be divided into: (5) initial construction of socialist industry in New China period (1950–1957), (6) the Second Five-Year Plan period (1958–1963) and (7) the Third Front Movement period (1964–1978). It should be noted that the beginning of China's early modern industrial history was 1840, whereas the development of early modern industry in Tianjin began in 1860 [26], so the first period was 1860–1894. Secondly, from an industrial history perspective, the fifth period includes national economic recovery period (1950–1952) and First Five-Year Plan period (1953–1957), but as both periods were relatively short and few industrial legacy sites remain (five and four respectively), they are combined into an initial construction of socialist industry in New China period. The number of industrial heritage sites in Tianjin was counted using the above time boundaries (Table 2).

**Figure 2.** Tianjin Industrial Heritage Census GIS Database (base map source: National Basic Geographic Information System).

**Table 2.** Statistics on industrial heritage in Tianjin by historical period.



#### **Table 2.** *Cont.*

By analysing the statistical results, a total of 111 sites of Tianjin's industrial heritage survived from 1860 to 1978, of which the main contributor is the early modern period, especially from 1914 to 1936, which is a side indication that it was the peak period of industrial development in Tianjin at that time. After the founding of the People's Republic of China in 1949, the focus of industrial development gradually moved to the inland and the southwest and northwest regions, and the importance of Tianjin diminished [30]. The number of industrial heritage sites decreased significantly, and the type shifted to mainly municipal types, such as sluices [35].
