*2.3. Study Area*

The spatial area of this study is China's provincial power grids, and the time span is 2005 to 2014. China's power grid is the largest artificial grid in the world, thus choosing it as an example can bring us more details than other countries. From 2005 to 2014, China's power grid has expanded rapidly since the significant development of the economy. The electricity consumption of China increased from 2323 TWh to 5328 TWh from 2005 to 2014. China has a significant imbalance spatial distribution between energy sources and developed level, i.e., most energy sources are distributed far from load hubs. For example, coal-based thermal plants mostly located in northwestern provinces, while hydropower plants are located in southwestern provinces. However, over half of the electricity is consumed by coastal developed regions i.e., Jing-Jin-Ji area, Yangtze River delta, and Guangdong. A large amount of electricity in China is thus generated in the southwestern and northwestern China and then delivered to the load hubs through transmission lines. Power transmission demand is

increasing rapidly in the decade, and the maturity of technologies and materials has encouraged the construction of ultra-high-voltage (UHV) transmission projects

Multi-policies have been implemented during the decade, which jointly affected the VWT network. From 2005 to 2010, a large amount of coal power plants were encouraged to construct in western provinces, including Shanxi, Shaanxi, Inner Mongolia, Guizhou, and Yunnan [35]. Then, according to the 12th Five-Year plan (2011–2015) for energy development, Xinjiang was added to the list. In the meantime, the plan encouraged more renewable power connected to the power grid and restricted the coal power generation in the eastern of China since climate change and air pollution [36]. Along with the expanding of electricity transmission, VWT embodied in electricity transmission also increased significantly from 2005 to 2014. A deep investigation of the evolution of the VWT network is vital. Besides, to distinguish the impacts posed by different policies posted on the evolution of the VWT network, we divided the time span into two periods, i.e., 2005 to 2010, 2010 to 2014.
