Salt Lake City and slightly smaller than London, making Perth the 67th largest urban area in the world. Perth is also the 50th least densely populated out of the 990 urban areas in the world with a population above 500,000. The metropolitan region is defined by the Planning and Development Act 2005 to include 30 local government areas, with the outer extent being the City of Wanneroo and the City of Swan to the north, the Shire of Mundaring, City of Kalamunda and the City of Armadale to the east, the Shire of Serpentine-Jarrahdale to the southeast and the City of Rockingham to the southwest, and including Rottnest Island and Garden Island off the west coast. This extent correlates with the Metropolitan Region Scheme, and the Australian Bureau of Statistics' Perth (Major Statistical Division). The metropolitan extent of Perth can be defined in other ways – the Australian Bureau of Statistics Greater Capital City Statistical Area, or Greater Perth in short, consists of that area, plus the City of Mandurah and the Pinjarra Level 2 Statistical Area of the Shire of Murray, while the Regional Development Commissions Act 1993 includes the Shire of Serpentine-Jarrahdale in the Peel region. Geology and landforms Perth is on the Swan River, named for the native black swans by Willem de Vlamingh, captain of a Dutch expedition and namer of WA's Rottnest Island, who discovered the birds while exploring the area in 1697. This water body was known by Aboriginal inhabitants as Derbarl Yerrigan. The city centre and most of the suburbs are on the sandy and relatively flat Swan Coastal Plain, which lies between the Darling Scarp and the Indian Ocean. The soils of this area are quite infertile. Much of Perth was built on the Perth Wetlands, a series of freshwater wetlands running from Herdsman Lake in the west through to Claisebrook Cove in the east. To the east, the city is bordered by a low escarpment called the Darling Scarp. Perth is on generally flat, rolling land, largely due to the high amount of sandy soils and deep bedrock. The Perth metropolitan area has two major river systems, one made up of the Swan and Canning Rivers, and one of the Serpentine and Murray Rivers, which discharge into the Peel Inlet at Mandurah. The Perth-Gingin Shrublands and Woodlands and Banksia Woodlands of the Swan Coastal Plain straddle the metropolitan area. Climate Perth