**7. Conclusions**

This study analyses the development direction of a smart city based on blockchain technology and cryptocurrency and uses a literature review to compare the six areas of blockchain in China and other countries. We included the hot spots and research preferences

of the application layer, contract layer, consensus layer, incentive layer, network layer and data layer of the blockchain, and found that China's research is more preference application of landing and industry, while international research is more preferred to the research of the underlying technology of finance and blockchain. Based on the analysis of cryptocurrencies and smart city, cryptocurrencies will get more market support in the future, and currently 'metaverse', 'DAO', 'NFT', 'Web 3.0' are developing rapidly, cryptocurrencies may be combined with smart cities to reshape the whole financial industry and network world. This paper introduces the concept of Kolmogorov entropy to cryptocurrencies and smart cities to measure the level of disorder within the system. This study is a qualitative study, and we will do more quantitative studies in the future to measure specific monetary entropy and Kolmogorov entropy, crypto-economic entropy, urban entropy, etc. The study may help scholars interested in blockchain to learn the basic knowledge of blockchain, and at the same time helps to understand the global hotspots of entropy and the research direction of entropy.

**Author Contributions:** Conceptualization, F.L. and J.-Y.Q.; methodology, F.L.; investigation, F.L. and H.-Y.F.; resources, F.L.; data curation, F.L.; supervision, F.L. and J.-Y.Q.; project administration, J.-Y.Q.; funding acquisition, J.-Y.Q. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work is supported by 2019, Digital Transformation in China and Germany: Strategies, Structures and Solutions for Ageing Societies, GZ 1570.

**Institutional Review Board Statement:** No applicable.

**Informed Consent Statement:** No applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** Thanks to the blockchain technology team of the Cross-Innovation Laboratory of East China Normal University for their fully support. At the same time, We also thank the reviewers for their valuable time.

**Conflicts of Interest:** The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
