The Seoul National Capital Area (SNCA) is a region located in the north-west of South Korea. It is generally referred to as Sudogwon in Korean, and contains three different administrative districts: Seoul, Incheon and a large part of Gyeonggi-do. The SNCA is technically distinct from the Seoul Metropolitan Area (SMA), as the former is a fixed entity, while the latter refers to places currently considered under the economic, industrial and cultural influence of Seoul. Since the extension of the Seoul Metropolitan Subway to Cheonan in Chungcheongnam-do, some have classified Cheonan as now within the SMA, but not within the SNCA. However, the terms SNCA, SMA and Sudogwon are largely analogous and used interchangeably. The Seoul National Capital Area has a population of 24.5 million (as of 2007) and is ranked as the second largest metropolitan area in the world. It forms the cultural, commercial, financial, industrial, and residential center of South Korea. The largest city is Seoul, with a population of approximately 10.2 million people, followed by Incheon, with 2.6 million.