## 5 Discussion and Conclusions  
This article presents a new approach for developing a GTM-based patent map to identify vacant technology fields and to design technology development strategies for promising vacant technology fields. Compared to other studies, this study has the advantage of objectively analyzing a future promising technology. Furthermore, networks designed on aspects of macro and micro can be utilized for technological development. The underlying concept is to identify vacant technology fields from a patent map and to then analyze any patent vacuums. The vacant technology fields are defined as undeveloped fields that are expected to be developable in the future. GTM-based patents through GTM's inverse mapping algorithm to analyze the vacant technology fields through reliable and objective information extraction to automatically generate a patent vacuum's core IPC. This is an important point on the GTM-based patent map. However, a vacant technology field may not have been developed for a variety of reasons, such as technical barriers or lost technology. Above all, the focus of this research is not limited to the development of patent maps but extends to confirming the potential of vacant technology fields. This study applies technical analysis to discover potential new technology opportunities and to explore those possibilities. Such a process is quantitative and objective because it measures the current technology level as a TAI and TII index, evaluates the current state of technology development, and applies time series analysis to reflect future trends. It can thus be used as the basis for objectively defining promising technical fields, i.e., these methods can be good sources of information for initiating new business creation. Finally, based on the above findings, we believe that the development of technologies related to freight transportation, transportation between ships and railways, and the maintenance of such technologies and vehicles will continue. Many companies and R&D organizations involved in technology need insights related to technology development and guidelines for those involved to make decisions for practical R&D strategies. This study provides the results of this study to provide guidelines for R&D stakeholders. We apply a network analysis to derive technology development strategies in the vacant technology field. To develop technology, it is necessary to investigate and analyze the technology in various aspects. This research analyzes macro and micro aspects and provides important insights into technological development. On the macroscopic side, from an IPC perspective, we identify the technology field that needs to be investigated/analyzed to design and develop networks. In addition, from the perspective of keywords that are important on the micro side, we design networks and analyze detailed technical relationships. We understand the significant technology keywords and confirm the technology elements that should be included in technology development. From various perspectives, network analysis can identify opportunities for new technologies, quantitatively analyze results, and establish technology development strategies. Therefore, this study provides important insights for researchers and developers in exploring technological opportunities. It can also be used as a sufficient basis for decision or policy makers to plan new content for technology development, and technology fusion can develop new technologies. Despite the advantages of this research, some limitations are in identifying vacant technologies. As aforementioned, IPC code can be employed to objectively extract significant results. However, an IPC can classify some broad technical fields that correspond to macro level. Based on these limitations, this study needs to be improved in the future. It is possible to analyze at a detailed level than the subclass through the classification system because it can be appropriate to identify more detailed and informative contents.