Addressing issues such as excessive dependence on desktop commercial software, high experience thresholds, and the inability to share and accumulate cartographic outputs in current transport planning thematic mapping, this paper designs and implements a lightweight online mapping system tailored for transport planning themes based on open source GIS technology solutions. The system encompasses functional modules such as convenient management of multi-source data, user space and permission division, personalized thematic mapping, map tools, and output saving and sharing. It addresses technical challenges such as rendering large files on the web, personalized font annotation, and complex style configuration. The system has been promoted and applied to transport planning institutes in Shenzhen, Shanghai, Wuxi, Wuhan, and other cities, serving as a work assistant for numerous transportation planners. It effectively supports the digital transformation of transport planning and demonstrates the convenience and practicality of the system.