Located along the Yellow Sea, Inchon is a city (center, right) of over 2 million people and is the chief port of Seoul, South Korea. The difference between high tide and low tide can vary up to 32 feet (9.75 meters). When the tide is out, vast stretches of mud flats remain, making it very difficult for ships to traverse the harbor. Seoul, the capital of South Korea, is located about 20 miles (32 km) to the northeast. The Demilitarized Zone, the area that separates North and South Korea, starts at the mouth of the river to the north of Inchon.