It makes sense to tax homeowners who leave their units vacant, since their decision to keep scarce property off the market is a waste that exacerbates the housing crisis.

The same applies to landowners who leave land vacant or underdeveloped when they could develop it into an apartment that alleviates the housing crisis.

It also makes sense to tax landlords who charge market rents. While tenants suffer from the shortage, it is landlords who reap unearned windfalls. While vacant property owners waste value every month that could benefit society, landlords capture that value for themselves, so the city should take a cut.

And if we charge landlords a tax for the high rents they collect, then we should also charge homeowners for the imputed rent they would have collected, to remove the inequity between owner-occupiers and landlords.

If we combine these 4 taxes, we would have a pretty good system for encouraging vacant landowners to use their land efficiently while also raising revenue from the landlords who benefit from the crisis. But then we would realize that the simpler solution is a higher, fairer property tax to begin with (by repealing Proposition 13).