Open big data from ticketing website as a useful tool for characterizing spatial features of the Chinese high-speed rail system

China now has the largest high-speed rail system in the world. However, due to data limitations, understanding of this system remains incomplete. Here we combined open big data, complex network indicators and spatial analyses to reveal the hierarchical and modular structure of the system. Many spatial features well coincide with the planning, while some interesting features may result from self-organization, including discrepancies between the actual and planned structure, displacement of regional railway hubs and mismatch between the spatial and network dimensions of system modularity. Open big data are to be further mined for better understanding this unique transportation system.