## 4 Bibliometric Analysis
### Science Mapping Analysis  
#### 4.3.1 Co-Citation Analysis  
The authors considered co-citation analysis to be one of the science mapping techniques. Paper C simultaneously cites published papers A and B, resulting in co-citation. In this subsection, the authors perform co-citation analysis on cited sources and cited authors to explore journal-to-journal and author-to-author correlations. When citing two sources or authors simultaneously, it means that they have the same field of research and interest. First, to analyze the co-citation network of cited sources, the authors set a threshold of at least 70 citations and finds 20 sources that meet this threshold. Table 7 lists the total co-citation link strength of these sources. The authors sort the table based on the total link strength of the journal. A source's total link strength is the sum of its link strengths with all other sources, while link strength refers to the frequency of co-citations between two sources in a third source. To better illustrate the link model, the authors generated the scientific landscape of the co-citation networks of the journals using the VOSviewer 1.6.20 software (Figure 6). Figure 6 divides the journal into two clusters (red and green), with each node in Figure 6 representing the corresponding source. The larger the node, the higher the co-citation, and the thicker the link between two nodes, the stronger the link strength between the two sources. The authors chose the total link strength as the weight for the co-citation analysis. Sources with higher citations have higher link strength, and it is interesting to note that all sources of each cluster are cited together with the sources of the clusters they are in. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Source** & **Citations** & **Total Link Strength** \\ \hline Computer-Aided Civil and Infrastructure Engineering (comput-aided civ inf) & 607 & 10694 \\ IEEE Transactions on Intelligent Transportation Systems (ieee t intell transp) & 483 & 9144 \\ \hline Proceedings CVPR IEEE (proc cvpr ieeee) & 443 & 8626 \\ \hline Automation in Construction (automat constr) & 434 & 8425 \\ \hline Journal of Computing in Civil Engineering (j comput civil eng) & 285 & 5571 \\ \hline Construction and Building Materials (constr build mater) & 322 & 5315 \\ \hline Lecture Notes in Computer Science (lect notes comput sc) & 236 & 4957 \\ \hline arXiv (arxiv) & 225 & 4472 \\ \hline IEEE Transactions on Pattern Analysis and Machine Intelligence (ieee t pattern anal) & 221 & 4335 \\ \hline IEEE International Conference on Image Processing (ieee image proc) & 221 & 4152 \\ \hline IEEE Access (ieee access) & 180 & 3714 \\ \hline Sensors (sensors-based) & 176 & 3233 \\ \hline IEEE Conference on Computer Vision and Pattern Recognition (ieee i conf comp vis) & 126 & 2919 \\ \hline IEEE Transactions on Image Processing (ieee t image process) & 115 & 2339 \\ \hline Transportation Research Record (transport res rec) & 132 & 2180 \\ \hline Pattern Recognition Letters (pattern recogn lett) & 109 & 2066 \\ \hline International Journal of Pavement Engineering (int j pavement eng) & 109 & 2012 \\ \hline Advances in Neural Information Processing Systems (adv neur in) & 73 & 1530 \\ \hline Advanced Engineering Informatics (adv eng inform) & 78 & 1498 \\ \hline Measurement Science and Technology (measurement) & 72 & 1470 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Co-citation indices of the sources. A closer look reveals that the red cluster contains a total of 11 sources, the most prominent of which is _IEEE Transactions on Intelligent Transportation Systems_ with 19 links and a total link strength of 9144. It has 134 citations for _Computer-Aided Civil and Infrastructure Engineering_, 115 citations for _Proceedings CVPR IEEE_, and 113 citations for _Automation in Construction_. This clearly shows that _IEEE Transactions on Intelligent Transportation Systems_ is highly relevant to these three journals in the field of vision-based road crack detection research.