Singapore, officially the Republic of Singapore, is a city-state located at the southern tip of the Malay Peninsula, about 85 miles (137 kilometres) north of the Equator. It consists of the diamond-shaped Singapore Island and some 60 small islets; the main island occupies all but about 18 square miles of this combined area. The main island is separated from Peninsular Malaysia to the north by Johor Strait, a narrow channel crossed by a road and rail causeway that is more than half a mile long. The southern limits of the state run through Singapore Strait, where outliers of the Riau-Lingga Archipelago—which forms a part of Indonesia—extend to within 10 miles of the main island.