Dataset of the South China Sea U-boundary and the Geographical Names for Part of the Nanhai Zhudao

Li, J. M.  Zhang, W. Z.  Liu, S. H.  Luo, Y.^*

China Aero Geophysical Survey and Remote Sensing Center for Natural Resources, Beijing 100083, China

Abstract: A dataset of the South China Sea (SCS) U-boundary (1948) was obtained by extracting coordinate information for the solid-line U-boundary delineated on the Map of East Indies reported in the Chinese Science Bulletin using geographic information system technology. A dataset of the geographical names of Nanhai Zhudao (the SCS Islands) was obtained by extracting the names from the Map of East Indies (and five other maps of the SCS published in the same period). As historical data relating to national boundary delimitation in the South China Sea, the two datasets have important implications for the investigation of the delineation and evolution of China’s maritime boundary in the SCS and will serve as important historical evidence for China to protect its territorial sovereignty and maritime rights and interests in the SCS.

Keywords: South China Sea U-boundary; geographic name; Map of East Indies; South China Sea Islands; South China Sea

DOI: https://doi.org/10.3974/geodp.2022.01.16

CSTR: https://cstr.escience.org.cn/CSTR:20146.14.2202.01.16

Dataset Availability Statement:

The dataset supporting this paper was published and is accessible through the Digital Journal of Global Change Data Repository at: https://doi.org/10.3974/geodb.2021.08.07.V1 or https://cstr.escience.org.cn/CSTR:20146.11.2021.08.07.V1; https://doi.org/10.3974/geodb.2021.09.06.V1or https://cstr.escience.org.cn/CSTR:20146.11.2021. 09.06.V1.

1 Introduction

China’s Nanhai Zhudao (the South China Sea Islands) consist of the Dongsha Islands, the Xisha Islands, the Zhongsha Islands and the Nansha Islands. China is the first to have discovered, named, and explored and exploited the South China Sea Islands and relevant waters, and the first to have exercised sovereignty and jurisdiction over them continuously, peacefully and effectively, thus establishing territorial sovereignty and relevant rights and interests in the South China Sea^[1]. The South China Sea (SCS) is rich in resources and has an extremely important strategic status. Territorial sovereignty and maritime boundary delimitation in the SCS are issues involving the core interests of China. Tang et al.^[2] rediscovered that on the New Map of the People’s Republic of China^[3] published in 1951 (on which China’s SCS U-boundary was delineated using the solid-line national boundary symbol), the SCS came under the jurisdiction of the South-Central Administrative Region. They verified that both the solid-line and the dashed-line U-boundary were then internationally recognized methods for the delineation of national maritime boundaries and proposed the use of the “South China Sea U-boundary” for describing China’s maritime boundary in the SCS. Tang et al. ^[4] also raised the problem of the zoning of the ecological environment along the SCS U-boundary. Luo et al.^[5] found another version of the national boundary delimitation in the SCS—also using the solid-line national boundary symbol—in the Map of East Indies^[6] and further explained the implications of China’s sovereignty over the SCS and the SCS U-boundary. As a major medium for representing national boundaries, maps are notable evidence of the formation and evolution of the U-boundary^[7]. The Map of East Indies is undoubtedly evidence for the boundary delimitation in the SCS. In this paper, based on the Map of East Indies, we provide a dataset for investigating the delineation and evolution of the U-boundary.

2 Metadata of the Dataset

The metadata of the Dataset of the SCS U-boundary and the names of the SCS Islands^[13,14] is summarized in Table 1. It includes the dataset full name, short name, authors, year of the dataset, spatial resolution, data format, data size, data files, data publisher, and data sharing policy, etc.

3 Methods

Raster image of the Map of East Indies published by the Shanghai Ya Kwang Geographical Institute in 1948 in both Chinese and English^[6] was digitized using ArcGIS software. Then the SCS U-boundary and the geographic names on this map were extracted into vector line data and text data. Finally, we obtained the SCS U-boundary (1948) and all the geographical names of islands, reefs, shoals, and cays on this map. Data processing is mainly composed of the following steps.

(1) Data source

The raster image of the Map of East Indies was obtained from the Library of Congress of the United States. This map is a colour map measuring 65 cm × 101 cm drawn at a scale of 1:6,000,000. The main map covers an area of east of 145°E, west of 95°E, south of 10°S, north of 20°N, shows Asia and Oceania, covering the entire area of the SCS^[5].

(2) Geographic coordinate system

Longitudes and latitudes are indicated on the map as perpendicular parallel straight lines, with the spacing 5°. On this basis, a graticule grid covering this area was created in ArcGIS as geographic reference coordinates. The China Geodetic Coordinate System (CGCS2000) was used.

(3) Preprocessing

The northernmost latitude line indicated on the Map of East Indies is 20°N, and the

Table 1  Metadata summary of the Dataset of the South China Sea U-boundary and the dataset of part of the names of the South China Sea Islands

graticules of 5° × 5° are incomplete at the north parts of the map. We added the uncomplete grids of the graticule to the northernmost latitude of 25°N. We also trimmed the image to remove the unnecessary part of the map, which is out of the graticules range of the SCS U-boundary.

(4) Map calibration

We used the graticules created in Step 2 as the reference grids for calibration and the graticule grid nodes as control points. The raster graphic obtained in Step 3 was calibrated using the Georeferencing tool of ArcGIS, and the final graticules of the raster graphic overlapped with the reference grids.

(5) Extracting U-boundary

The SCS U-boundary line was vectorized, thereby obtaining a vector file containing accurate location data for this boundary.

(6) Extracting the geographical names

The names of all islands, reefs, shoals, and cays indicated on the following six maps were compiled and compared in Table 2 and 3: (i) Map of East Indies (1948)^[6]; (ii) Location Map of the SCS Islands (1:4,000,000) published by the Territorial Administration Division of the Ministry of Interior of the Republic of China in 1947^[7–9]; (iii) Location Map of the SCS Islands (1:8,500,000) contained in A Brief Account of the Geography of the SCS Islands (1947)^[10]; (iv) Location Map of the SCS Islands (1:9,100,000) contained in the Map of the Administrative Districts of the Republic of China (1948)^[11]; (v) Map of the Hainan Island and the SCS Islands (1:10,000,000) contained in the New Maps of Chinese Provinces (1948)^[12]; and (vi) Map of the SCS Islands (1:15,000,000) contained in the New Map of the People’s Republic of China (1950)^[3].

4 Data Results and Validation

4.1 Data Composition

Dataset 1: This consists of a digital scan of the original copy of the Map of East Indies (.tif format) and a vector file of the SCS U-boundary (1948) (.shp and .kmz formats). The total file size is 280 MB.

Dataset 2: This includes a text table (.xlsx format) of all geographical names on the Map of East Indies and the other five maps of the SCS Islands published in the same period. The file size is 16.7 KB.

4.2 Data Products

(1) Digitized dataset of the SCS U-boundary (1948)

The Map of East Indies uses the solid-line national boundary symbol to delineate China’s maritime boundary in the SCS. The SCS Islands are all enclosed within this boundary. The names of the SCS Islands are marked using Chinese names, and four Chinese characters—“中华民国” (the Republic of China) are marked over the waters enclosed by the boundary^[5]—that proclaim China’s sovereignty over the South China Sea. Accurate vector information of the SCS U-boundary on the Map of East Indies was obtained by vectorizing.

(2) Dataset of the names of the SCS Islands (1940s–1950s)

The names of all islands, reefs, shoals and cays on the Map of East Indies (1948)^[6] and the other five maps published in the same period are shown in Tables 2 and 3. All these geographical names (some old names) are included in the Standard Geographical Names for part of Nanhai Zhudao published by the China Geographical Names Committee under the authorization of the State Council of the People’s Republic of China in April 1983^[16]. The dataset of geographic names shows that the Map of East Indies is consistent with two kinds of the Location Map of the SCS Islands. The only difference is that China’s maritime boundary in the SCS is delineated on the Map of East Indies using the solid-line national boundary symbol.

4.3 Data Validation

Map calibration was performed using the Georeferencing tool of ArcGIS. Using the graticules nodes of the pretreated raster graphic as the source control points and the graticules nodes of the CGCS2000 coordinate system as the target control points, 30 pairs of points were sampled for calibration and correction with the spline method. The final total error was of the order of magnitude 1.0 × 10⁻¹¹. After the processing, the nodes and the longitudinal and latitudinal lines of the two graticules overlapped.

5 Discussion and Conclusion

As another representation of the map of the SCS Islands, the Map of the East Indies delineates the SCS U-boundary using the solid-line national boundary symbol and clearly

Table 2  List of completely consistent geographical names on the Map of East Indies and five other maps of the South China Sea Islands

Table 3  List of inconsistent geographical names on the Map of East Indies and five other maps of the South China Sea Islands

(To be continued one the next page)

 (Continued)

Note: “-” indicates that the geographic name is not used on a map, and the maps indicated by Roman numerals in the header are listed in section 3.

indicates the national boundary delimitation in the SCS in 1948. The map clearly indicates China’s territorial sovereignty over the SCS Islands and is historical evid­ence of China’s territorial sovereignty and maritime rights and interests in the SCS.

In this study, a digitized dataset of the SCS U-boundary delineated on the Map of East Indies published by the Ya Kwang Geographical Institute in 1948 was obtained (Figure 1). The geographical names on the Map of East Indies were compared with those on five other maps of the SCS Islands published in the same period, thereby obt­aining the Dataset of Geographical Names of Islands from Six Maps Covering the SCS Published from the 1940s to the 1950s.

Our results show that the following maps of the same origin in the delineation of China’s territory in the South China Sea: the Map of East Indies (published in January 1948), the Location Map of the SCS Islands contained in A Brief Account of the Geography of the SCS Islands (published in November 1947), the Location Map of the SCS Islands contained in the Map of the Administrative Districts of the Republic of China (produced in December 1947 and published in February 1948). The only difference is that China’s maritime boundary in the SCS is delineated on the Map of East Indies using the solid-line national boundary symbol. These two datasets have important implications for the investigation of the national boundary delimitation and evolution in the SCS and will serve as basic data and important evidence for research into the SCS problem.

Author Contributions

Li, J. M. formulated the overall design for the data development and collected and treated the data of the SCS U-boundary (1948). Luo, Y. extracted some of the names of the SCS Islands on the maps. Liu, S. H. and Zhang, W. Z. performed data verification. Li, J. M., Zhang, W. Z., Liu, S. H., and Luo, Y. co-authored the paper.

Conflicts of Interest

The authors declare no conflicts of interest.

References

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