Rouge River (Ontario) in the context of "Rouge National Urban Park"

Scarborough (/ˈskɑːrbʌroʊ/; 2021 Census 629,941) is a district of Toronto, Ontario, Canada. It is situated in the eastern part of the City of Toronto. Its borders are Victoria Park Avenue to the west, Steeles Avenue and the city of Markham to the north, Rouge River and the city of Pickering to the east, and Lake Ontario to the south. Scarborough was named after the English town of Scarborough, North Yorkshire, inspired by its cliffs.

Scarborough, which was settled by Europeans in the 1790s, has grown from a collection of small rural villages and farms to become fully urbanized and diverse cultural community. Incorporated in 1850 as a township, the district became part of Metropolitan Toronto in 1953 and was reconstituted as a borough in 1967. The borough rapidly developed as a suburb of Toronto over the next decade and became a city in 1983. In 1998, the city and the rest of Metropolitan Toronto were amalgamated into the present city of Toronto. The Scarborough Civic Centre – the former city's last seat of government – now houses offices of the municipal government of Toronto.

The Municipality of Metropolitan Toronto was an upper-tier level of municipal government in Ontario, Canada, from 1953 to 1998. It was made up of the old city of Toronto and numerous townships, towns and villages that surrounded Toronto, which were starting to urbanize rapidly after World War II. It was commonly referred to as "Metro Toronto" or "Metro".

Passage of the 1997 City of Toronto Act caused the 1998 amalgamation of Metropolitan Toronto and its constituents into the current City of Toronto. The boundaries of present-day Toronto are the same as those of Metropolitan Toronto upon its dissolution: Lake Ontario to the south, Etobicoke Creek and Highway 427 to the west, Steeles Avenue to the north, and the Rouge River to the east.

The geography of Toronto, Ontario, covers an area of 630 km (240 sq mi) and is bounded by Lake Ontario to the south; Etobicoke Creek, Eglinton Avenue, and Highway 427 to the west; Steeles Avenue to the north; and the Rouge River and the Scarborough–Pickering Townline to the east. In addition to Etobicoke Creek and the Rouge River, the city is trisected by two minor rivers and their tributaries, the Humber River in the west end and the Don River east of downtown. Both flow southward to Lake Ontario at Humber Bay and Toronto Harbour respectively, which are part of the longer Waterfront, as well as Etobicoke Creek and the Rouge River.

The concentration and protection of Toronto's many deep ravines allows for large tracts of densely forested valleys with recreational trails within the city. Approximately 26 to 28 percent of Toronto is covered with over ten million trees, a fairly high percentage within a large city in North America and there are ambitious proposals to double the coverage. Some parts of Toronto, such as High Park, Swansea and the lower Humber River, are located in the northernmost reaches of the Carolinian forest zone found in North America.