[dstainer]

You can do (or I guess proposed to do) what Vancouver did, tax vacant properties. Foreign buyers would purchase homes and then let them sit, reducing inventory and raising prices.

http://www.cbc.ca/news/canada/british-columbia/vancouver-vac...

[bufordsharkley]

This is certainly a low-hanging fruit to attack, but one can get to the point where land is inefficiently used, even if it's completely occupied.