Taxing used property in dense areas would likely just increase the costs further, although I assume that might be intended in the long run to push for more use

Taxing used property in dense areas would likely just increase the costs further, although I assume that might be intended in the long run to push for more use of vertical space. More useful would be a tax which increases the longer a vacancy exists on unused lots, vacant or secondary apartments/housing, and property sales that have been unsold for X number of days. Real estate speculation and housing as financial instruments are basically contemporary feudalism.