## 4 Experiment Results and Visualization
### Abstract Clustering Results and Visualization
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \multicolumn{2}{c}{**1 st Iteration**} & \multicolumn{2}{c}{**2 nd Iteration**} & \multicolumn{2}{c}{**3 rd Iteration**} & \multicolumn{2}{c}{**4 th Iteration**} \\ \hline
**Number of Abstracts** & **Silhouette Score** & **Number of Abstracts** & **Silhouette Score** & **Number of Abstracts** & **Silhouette Score** & **Number of Abstracts** & **Silhouette Score** \\ \hline \hline (\#1) 16 & 0.99 & & & & & & \\ \hline (\#2) 21 & 0.88 & & & & & & \\ \hline (\#3) 38 & 0.74 & & & & & & \\ \hline (\#4) 31 & 0.69 & & & & & & \\ \hline (\#5) 31 & 0.51 & & & & & & \\ \hline \multirow{2}{*}{62} & \multirow{2}{*}{0.77} & \multicolumn{2}{c}{(\#6) 23} & \multicolumn{2}{c}{0.85} & \multirow{2}{*}{0.67} & \multirow{2}{*}{0.7} & \multirow{2}{*}{0.7} & \multirow{2}{*}{0.7} \\ \cline{3-3} \cline{5-6}  & & & (\#7) 25 & & & & \\ \cline{3-3} \cline{5-6}  & & & (\#8) 14 & & & & \\ \hline \multirow{2}{*}{107} & \multirow{2}{*}{0.71} & \multicolumn{2}{c}{(\#9) 33} & \multicolumn{2}{c}{0.87} & \multirow{2}{*}{0.7} & \multirow{2}{*}{0.7} & \multirow{2}{*}{0.7} \\ \cline{3-3} \cline{5-6}  & & & (\#10) 42 & & & & \\ \cline{3-3} \cline{5-6}  & & & (\#11) 32 & & & & \\ \hline \multirow{2}{*}{593} & \multirow{2}{*}{0.76} & \multicolumn{2}{c}{(\#13) 12} & \multirow{2}{*}{0.82} & \multirow{2}{*}{0.66} & \multirow{2}{*}{0.7} & \multirow{2}{*}{0.7} \\ \cline{3-3} \cline{5-6}  & & & (\#14) 23 & & & & \\ \cline{3-3} \cline{5-6}  & & & (\#15) 17 & & & & \\ \cline{3-3} \cline{5-6}  & & & (\#16) 35 & & & & \\ \cline{3-3} \cline{5-6}  & & & 187 & \(-\)0.50 & & & \\ \cline{3-3} \cline{5-6}  & & & & (\#17) 10 & & & \\ \cline{3-3} \cline{5-6}  & & & (\#18) 15 & & & & \\ \cline{3-3} \cline{5-6}  & & & (\#19) 25 & & & & \\ \cline{3-3} \cline{5-6}  & & & & (\#20) 12 & & & \\ \cline{3-3} \cline{5-6}  & & & & (\#21) 19 & & & \\ \hline \multirow{2}{*}{106} & \multirow{2}{*}{\(-\)0.48} & \multirow{2}{*}{\(-\)0.48} & \multirow{2}{*}{\(\#23) 34} & \multirow{2}{*}{0.31} & \multirow{2}{*}{0.48} & \multirow{2}{*}{0.02} \\ \cline{3-3} \cline{5-6}  & & & & (\#24) 46 & & & \\ \hline \end{tabular}
\end{table} 
Table 2: The results of four iterations of abstract clustering. Each abstract cluster is labeled with a sequence number #1, #2, and #3, etc. the orange dots the cluster #9, #10, and #11. The 287 outliers from the first iteration are colored in gray. It is interesting that these outliers are clustered in three areas, where the left region is the cluster #12 to 16#, the middle is cluster #22 to #24, and the right is cluster #17 to #21. Clicking on a cluster's color region on the scatter plot, say blue, displays seven subsequent abstract clusters (the right panel in Figure 5). These clusters are represented in a list, where they are formatted using the JavaScript open-source Pagination ([[https://pagination.js.org/index.html](https://pagination.js.org/index.html)]([https://pagination.js.org/index.html](https://pagination.js.org/index.html)), accessed on 1 January 2022) and CSS Bootstrap ([[https://getbootstrap.com/](https://getbootstrap.com/)]([https://getbootstrap.com/](https://getbootstrap.com/)), accessed on 1 January 2022) libraries. Each abstract cluster shows its silhouette scores and a list of representative terms to provide an overview of this cluster. Terms (two-word compound nouns) are extracted from the abstracts in a cluster and ranked by a score summing up the frequency and range, where the frequency is the total number of occurrences of a term and the range is the total number of abstracts that a term appears in for the cluster. We focus on compound nouns of two words because nouns are content words that convey the meaning and compound nouns carry more specific meaning than single nouns. The top of the right panel in Figure 5 shows nine common terms in the blue cluster and some of these terms, such as _machine learning_, _urban data_, _urban design_, and _urban planning_, are the terms that we used to search the abstracts in Scopus.