宣光省
Its exact location is at 21°21’ to 21°42’ North latitude, 105°23’ to 105°44’ East longitude. It spans a large area along the Tam Đảo range and administratively belongs to 6 districts and 1 city: Lập Thạch, Tam Dương, Bình Xuyên and the city of Vĩnh Yên of Vĩnh Phúc Province; Sơn Dương of Tuyên Quang Province; Đại Từ and Phổ Yên of Thái Nguyên Province.