# Reshaping the Digital Twin Construct with Levels of Digital Twinning (LoDT)
## 4 Assessing the Level of Digital Twinning (LoDT)
### Summary and Additional Observations  
Table 5 summarises the relationship between the structural elements of the DT concept, the phases of the digital twinning functional architecture, and the corresponding dimensions.  
In addition to the dimensions previously discussed, connectivity between DTs is also a relevant and frequently mentioned topic in the literature. According to prominent perspectives, a DT of a specific physical entity can be connected to other DTs, from which it can extract more and better information to generate greater value for the set of assets in question and the services they provide [67]. This is particularly relevant in the case of networked asset systems.  
Emerging projects related to smart cities and national-level DTs make the discussion about connectivity and federation even more significant. The structure in which DTs are constructed and then integrated into organisational systems can vary depending on the  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multicolumn{2}{c}{**DT Element**} & \multicolumn{1}{c}{**Architecture Phase**} & \multicolumn{1}{c}{**Dimension**} \\ \hline Physical entity & & Hierarchy \\ \hline \multirow{3}{*}{Data} & \multirow{3}{*}{Creation} & Connection \\ \cline{2-2} \cline{3-3}  & Communication & Synchronization \\ \cline{2-2} \cline{3-3}  & Integration & Non-geometric representation \\ \hline \multirow{3}{*}{Digital models} & Analysis & Intelligence \\ \cline{2-2} \cline{3-3}  & Perception & Geometric representation \\ \cline{2-2} \cline{3-3}  & \multirow{2}{*}{Interface} \\ \cline{2-2} \cline{3-3} Decision making & Decision & \\ \cline{2-2} \cline{3-3}  & Action & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Correspondence between DT elements and digital twinning phases and dimensions.  
purpose and context of each. There can be an ecosystem of connected and federated DTs, as well as a DT of various connected physical asset systems.  
Nevertheless, it is essential to clarify that the concept of a National Digital Twin (NDT) will never truly be achieved because not all physical space will be or can be digitally twinned, and not all digital models will be federated. On the one hand, physical space is continually evolving, and only a portion of it is useful to represent. On the other hand, connectivity between various digital models should serve a specific purpose and should only occur when the generated value justifies it [26], meaning that not all models should be connected. An NDT will always result from the digital twinning of several physical entities within its scope, whose models are federated into groups according to the various defined purposes. The significant challenge of a NDT lies in ensuring interoperability among all these elements, rather than whether all physical entities in the real world are represented or their models are federated. The connectivity and federation of digital twins also bring other challenges, including data storage, security, and information sharing.  
Therefore, security, ownership, resilience, and interoperability requirements must be incorporated from the beginning of digital twinning strategies [67; 100]. As an example, there are ongoing efforts to leverage blockchain technology to ensure data integrity and increase trust in data transactions in collaborative construction environments [101].