# CiteSpace-Based Bibliometric Review of Pickup and Delivery Problem from 1995 to 2021
## 4 Visualization Results and Bibliometric Analysis Based on CiteSpace  
### Author and Cited Author Analysis  
In this section, we make the bibliometric and visualization analysis of author and cited author by setting the node type as \"author\" and \"cited author\" respectively in CiteSpace. The purpose of author analysis is to find the scholar who has the most publications, and to display the collaboration relationship between different scholars in the research. Generally, the more papers he or she published, the stronger ability to speed up the development of this study. The results of cited author analysis can help us not only identify the scholar who has the most academic level and academic influence, but also clarify the complicated co-citation relationship between authors. After running the software, the main results obtained are collaboration network map and co-citation network map of authors, which are shown in Figures 4 and 5 respectively. Table 3 lists and compares the distribution of the top 10 high-published authors and high-cited authors. \begin{table}
\begin{tabular}{c c c c} \hline
**No.** & **Number of Papers** & **The Percentage of Total** & **Category** \\ \hline
1 & 415 & 50.67\% & Operations Research \& Management Science \\
2 & 369 & 45.05\% & Computer Science \\
3 & 336 & 41.03\% & Engineering \\
4 & 147 & 17.95\% & Business \& Economics \\
5 & 146 & 17.83\% & Transportation \\
6 & 142 & 17.34\% & Transportation Science \& Technology \\
7 & 141 & 17.22\% & Computer Science, Interdisciplinary Applications \\
8 & 140 & 17.09\% & Computer Science Artificial Intelligence \\
9 & 135 & 16.48\% & Engineering, Industrial \\
10 & 102 & 12.45\% & Computer Science, Theory \& Methods \\ \hline \end{tabular}
\end{table} 
Table 2: Distribution of the top 10 categories in the research on PDP. \begin{table}
\begin{tabular}{c c c c c c} \hline
**No.** & \multicolumn{3}{c}{**High-Published Authors**} & \multicolumn{3}{c}{**High-Cited Authors**} \\ \cline{2-5}  & **Count** & **Author** & **Institution** & **Freq.** & **Cited Authors** & **Institution** \\ \hline
1 & 23 & [PERSON] & HEC Montreal & 260 & [PERSON] & HEC Montreal \\
2 & 13 & [PERSON] & HEC Montreal & 237 & [PERSON] & Technical University \\
3 & 13 & [PERSON] & University of Modena and & & & of Denmark \\  & & & & & 199 & [PERSON] & HEC Montreal \\
4 & 12 & [PERSON]. [PERSON] & Eindhoven University & & 198 & MWP[PERSON] & Georgia Institute \\  & & & & & & of Technology \\
5 & 11 & [PERSON] & National University & & 177 & [PERSON] & Polytechnique Montreal \\
6 & 11 & [PERSON] & Chongqingliatop & & 170 & [PERSON] & University of Bologna \\
7 & 10 & CK. [PERSON] & National Chung Cheng & & 143 & [PERSON]. [PERSON] & Johannes Kepler \\  & & & & & & University Linz \\
8 & 10 & [PERSON] & University Bourgogne & & 125 & [PERSON] & Northeastern University \\  & & & & & & \\
9 & 9 & [PERSON] & Fluminense Federal & & 110 & [PERSON] & Centre de Recherche sur \\  & & & & & & \\
10 & 9 & [PERSON] & University Bourgogne & & & \\  & & & & & \\  & & & & & & \\ \end{tabular}
\end{table} 
Table 3: The top 10 high-published authors and high-cited authors in the research on PDP. Figure 4 consists of 1732 nodes and 2782 links, where each node represents an author, each link represents a collaboration relationship between two authors. Moreover, the value of entire network's density is only 0.0019, which indicates the research direction of these authors are relatively scattered, and few connections and collaborations between them. Combining the results in Table 3, it is obvious that [PERSON] is the most productive author with 23 publications, who mainly focused on the areas of vehicle routing, location, and social network. Figure 4: Collaboration network map of authors in the research on PDP. Figure 5: Co-citation network map of authors in the research on PDP. districting, and timetabling [24; 25]. Followed by [PERSON], who is also the most cited author.