Group 1 - The core idea of the articles is the rapid development of cross-city metro systems in the Guangdong-Hong Kong-Macao Greater Bay Area, particularly focusing on the integration of Shenzhen and Dongguan through new metro lines [1][5][7] - Shenzhen is enhancing its metro connectivity with Dongguan by extending lines 10 and 11, and connecting them with Dongguan's metro lines, which will facilitate daily commutes for over a million people [1][5] - The Greater Bay Area's urban integration is exemplified by the opening of the Guangfo South Ring and the Fodong intercity railways, creating a transportation network that connects multiple cities and significantly reduces commuting times [3][5] Group 2 - The concept of "cross-city metro" is emerging in China's metropolitan areas, characterized by interconnected metro systems and efficient transfer hubs, allowing residents to travel between cities as easily as within districts [5][7] - Shenzhen's urban planning includes 11 cross-city rail lines that are under construction, aiming to enhance the connectivity and integration of the Shenzhen metropolitan area [5][7] - The construction of the Shenzhen Airport East Station, which will be a major hub for air and rail transport, is expected to facilitate rapid transfers and improve overall transportation efficiency in the Greater Bay Area [7]