Our southern Ontario map is provided by Google Inc and, like all Google maps, can be zoomed to street level and panned four ways to pick up the parts of southern Ontario that are hiding off the page.
Of Ontario's about 9 million people, you can be sure 7 million live in this part so there's too much detail for a static map to work on the page.
Southern Ontario runs from Sarnia and Windsor in the west to Cornwall in the east, that much is easily agreed on by Ontario's inhabitants. Where it gets difficult is to the north.
Ontario is still fairly well populated up to the Sudbury area but most Ontarians don't count that region as the south. Parry Sound too is a long way south of Sudbury and would make another good potential cut-off, the land is Canadian Shield around there but it's still within a reasonable drive from Toronto, say 3.5 hours depending on the time of day and the traffic.
Most Ontarians; however, think of a line from about Barrie to Ottawa as the dividing line. It's the edge of the Shield, with its bare rock surface and firs and birches, that makes it so. Below that line the land is farmable, above it not so much. It's 'the north', a land of lakes and forests, a place for active vacations like snowmobiling or huntin', shootin' n fishin' -- and, of course, fantastic photos.