This paper constructs an evaluation index system for the high-quality development of the marine economy based on the five dimensions of the new development paradigm. It employs entropy method, kernel density analysis, and Dagum Gini coefficient method to analyze the high-quality development level of China's marine economy and its spatial-temporal evolution from 2013 to 2022. The findings reveal that: (1) The comprehensive index for the high-quality development of China's marine economy exhibits an overall fluctuating upward trend; (2) The high-quality development levels of the marine economy in the eastern and southern marine economic circles are both above the national average, while that in the northern marine economic circle is below the national average; (3) The focus of high-quality development in China's marine economy is shifting towards economically developed regions along the southeast coast, demonstrating a trend of "higher in the south and lower in the north." Moreover, the gap in high-quality development of the marine economy among the three major marine economic circles is gradually narrowing, and the high-quality development of regional marine economies tends to become more coordinated.

In the mid-1990s, the concept of smart growth emerged in the United States as a critical response to the phenomenon of suburban sprawl. To promote sustainable urban development, it is necessary to further investigate the principles and applications of smart growth. In this paper, we proposed a Smart Growth Index (SGI) as a standard for measuring the degree of responsible urban development. Based on this index, we constructed a comprehensive 3E evaluation model—covering economic prosperity, social equity, and environmental sustainability—to systematically assess the level of smart growth. For empirical analysis, we selected two medium-sized cities from different continents: Wuhu County, China, and Colima, Mexico. Using an improved entropy method, we evaluated the degree of smart growth in recent years and analyzed the contributions of various policies to sustainable urban development. Then, guided by the ten principles of smart growth, we linked theoretical insights to practical challenges and formulated a development plan for both cities. To forecast long-term trends, we employed trend extrapolation based on historical data, enabling the prediction of SGI values for 2020, 2030, and 2050. The results indicate that Wuhu demonstrates a greater potential for smart growth compared with Colima. We also simulated a scenario in which the population of both cities increased by 50 percent and then re-evaluated the SGI. The analysis suggests that while rapid population growth tends to slow the pace of smart growth, it does not necessarily exert a negative impact on the overall trajectory of sustainable development. Finally, a study on the application of Transit-Oriented Development (TOD) theory in Wuhu County was conducted. Based on this analysis, we proposed several policy recommendations aimed at enhancing the city’s sustainable urban development.