The Provincial Highway Network consists of all the roads in Ontario maintained by the Ministry of Transportation of Ontario (MTO), including those designated as part of the King's Highway, secondary highways, and tertiary roads. Components of the system—comprising 16,900 kilometres (10,500 mi) of roads and 2,880 bridges —range in scale from Highway 401, the busiest highway in North America, to unpaved forestry and mining access roads. The longest highway is nearly 2,000 kilometres (1,200 mi) long, while the shortest is less than a kilometre. Some roads are unsigned highways, lacking signage to indicate their maintenance by the MTO; these may be remnants of highways that are still under provincial control whose designations were decommissioned, roadway segments left over from realignment projects, or proposed highway corridors.

Southern Ontario is a primary region of the Canadian province of Ontario. It is the most densely populated and southernmost region in Canada, with approximately 13.5 million people, approximately 36% of Canada's population of 37 million. The region lies south of the province's other primary region, Northern Ontario, although the exact northern boundary of Southern Ontario is disputed. However, its core region is situated south of Algonquin Park, the latter being in an area of transition between coniferous forest north of the French and Mattawa Rivers and southern deciduous forest. It covers between 14 and 15% of the province, depending on the inclusion of the Parry Sound and Muskoka districts which also lie in the transitional area between northern and southern forest regions. Southern Ontario differs greatly from Northern Ontario, having a much higher population density, a different climate, and a different culture than its northern counterpart. It is broken into smaller subregions, including Central Ontario, Eastern Ontario, the Golden Horseshoe, and Southwestern Ontario.