# CiteSpace-Based Bibliometric Review of Pickup and Delivery Problem from 1995 to 2021
## 4 Visualization Results and Bibliometric Analysis Based on CiteSpace
### Country and Institution Analysis  
To confirm the contribution and influence of each country/institution, examine the mutual collaboration relationship between different countries/institutions better, we employ CiteSpace to conduct country and institution analysis by setting the node type as \"country\" and \"institution\", respectively. First of all, the collaboration network map of countries is shown in Figure 7, where each circle represents a country, each link represents the collaboration relationship between countries. Next, the collaboration network map of institutions is shown in Figure 8, where each node denotes a research institution, each link denotes the collaboration relationship between two institutions. Tables 5 and 6 display the top 10 high-published countries between 1995 and 2021 and the top 10 high-published institutions between 1995 and 2021, respectively. \begin{table}
\begin{tabular}{c c c c c} \hline
**No.** & **Citation** & **Centrality** & **SSCI/SCIE** & **Cited Journals** & **Impact Factor** \\ \hline
1 & 676 & 0.01 & SCIE & European Journal of Operational Research & 4.213 \\
2 & 621 & 0.00 & SSCI; SCIE & Transportation Science & 3.384 \\
3 & 589 & 0.05 & SCIE & Computers \& Operations Research & 3.424 \\
4 & 443 & 0.00 & SSCI & Operations Research & 2.430 \\
5 & 326 & 0.02 & SCIE & Networks & 2.602 \\
5 & 322 & 0.03 & SSCI; SCIE & Transportation Research Part B-methodological & 4.796 \\
6 & 272 & 0.18 & SCIE & Computers \& Industrial Engineering & 4.135 \\
8 & 257 & 0.02 & SSCI; SCIE & Journal of The Operational Research Society & 2.175 \\
9 & 238 & 0.03 & Null & Lecture Notes in Computer Science & Null \\
10 & 222 & 0.04 & SCIE & Annals of Operations Research & 2.583 \\ \hline \end{tabular}
\end{table} 
Table 4: The top 10 high-cited journals. Figure 6: Co-citation network map of journals in the research on PDP. Figure 8: Collaboration network map of institutions in the research on PDP. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **Count** & **Centrality** & **Year** & **Country** \\ \hline
1 & 168 & 0.19 & 2003 & China \\
2 & 111 & 0.54 & 1995 & USA \\
3 & 68 & 0.16 & 2001 & France \\
4 & 62 & 0.24 & 1996 & Canada \\
5 & 57 & 0.05 & 2000 & Germany \\
6 & 47 & 0.10 & 2003 & Italy \\
7 & 42 & 0.13 & 1995 & Netherlands \\
8 & 33 & 0.05 & 2003 & Spain \\
9 & 32 & 0.05 & 2008 & Brazil \\
10 & 29 & 0.04 & 1998 & Norway \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The top 10 high-published countries between 1995 and 2021. Figure 7: Collaboration network map of countries in the research on PDP. According to Figure 7 and Table 5, China is the most productive country in the world, which has published 168 papers that accounts for about 20.52% of the total number of documents published from 1995 to 2021. Therefore, we can observe that China has developed rapidly and achieved rich results so far, although its PDP-related research work started relatively late compared to other countries. USA as one of the first countries to analyze the PDP, occupies the second position with 111 publications. From the perspective of country composition in Table 5, except for China and Brazil, the other productive countries are from Europe and North America, divergent academic cooperation relationship between countries is still weak and loose. As shown in Table 6, there are three Chinese institutions (Chongqing Jiaotong University, Beijing Jiaotong University, and City University of Hong Kong) in the top 10 high-published institutions, which coincides with the conclusion that China holds the first position among all countries in the world, in terms of the number of publications. However, the most influential institution is HEC Montreal located in Canada, which has published 31 documents that is approximately equal to the total 32 publications produced by Brazil.