Changan is headquartered at the intersection of Chongqing Yangtze River and Jialing River, and has jurisdiction over Chongqing Changan Automobile Co., Ltd., Changan Suzuki Automobile Co., Ltd., Changan Ford Mazda Automobile Co., Ltd., Changan Ford Mazda Nanjing Company, Changan Ford Mazda Engine Company, Nanjing Changan Automobile Co., Ltd., Hebei Changan Automobile Co., Ltd., Baoding Changan Bus Manufacturing Co., Ltd. and Chongqing Changan Crossing Vehicle Co., Ltd.
Chang 'an is just a town in Dongguan. I have never heard of other places called Chang 'an (not counting Xi 'an).