Study on Interactions between Urban Extension and Urban Metro Construction in Tianjin Built-Up Area

Urban extension is a direct reflection of the development of urbanization. The analysis of dynamic changes of urban extension can provide effective support for the government's decision-making for sustainable development. Urban metro constructions in major cities have started, and its impacts on urban development are also of great concern. Taking Tianjin built-up area as an example, this article first explored the urban expansion over two time spans during 15 years from 1993 to 2008, for which multi-source images were acquired for change detection. Results of classification were unified to two-value map of built and non-built areas in the same spatial resolution. Then the relationship between urban extension and metro planning was analyzed through overlaying the results together with vectors of subway distribution, which was achieved by vectoring Tianjin metro planning map. Different buffering areas were extracted for metro stations and overlaid with the urban extension areas for spatial analysis, which shows that there exists high correlativity between metro construction and urban expansion. Urban expansion in Tianjin results in more people and more traffic, so that it calls for metro construction to alleviate traffic pressure, while, on the other hand, metro lines play an engine of directing the pattern of urban expansion. Based on the relationship reached in this article, a brief prediction of the future urban expansion of Tianjin built-up area was made according to the construction time plan of new metro lines.