Toronto has a sprawl wall around it. Its called the Greenbelt.
The province passed a law, a number of years back, drawing the line beyond which 'urban' boundaries could not grow. Reserving the greenbelt to farms, nature, limited industry [[quarries) and grandfathered uses.
A link to the maps/area here:
http://www.greenbelt.ca/maps
On the whole, it has worked well, and is very popular.
The limitations are that the area isn't so large that developers can't leapfrog it in places. [[and are), as well as those who question the role this is having in Toronto's ever spiraling house prices [[up 33% in the last year).
However, it should be noted, Toronto still has lots of whitebelt [[areas not yet developed, but zoned for literally more than 100,000 acres of single family homes. So I think that's a pretty specious linkage.
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